The Categories
The Categories
Book Overview
Around 350 BCE, Aristotle sat down and tried to answer a question so basic it’s almost embarrassing: what are the different kinds of things you can say about anything? Not what’s true or false — that comes later. Just: when you open your mouth and describe something in the simplest possible way, what type of description are you giving?
His answer was a list of ten categories — substance, quantity, quality, relation, place, time, position, state, action, affection — and a short treatise explaining how they work. That’s this book. It’s barely thirty pages long, reads like lecture notes that were never fully polished, and has shaped how Western civilization thinks about classification, language, and reality for over two millennia. Not bad for a pamphlet.
The Categories falls into three parts. First, a preamble (Chapters 1-3) where Aristotle cleans his tools — defining terms, distinguishing types of predication, and then listing the ten categories themselves with examples drawn from everyday Athenian life. Second, the main event (Chapters 4-8), where he examines the most important categories in detail: substance gets the royal treatment as the foundation everything else rests on, followed by careful analyses of quantity, relation, and quality. Action, affection, and the remaining categories get a brief wave. Third, the “post-predicaments” (Chapters 9-12), where he steps back from individual categories to examine concepts that cut across all of them — types of opposition, what it means for one thing to come “before” another, the kinds of motion, and the surprisingly many things we mean when we say we “have” something.
What follows is a chapter-by-chapter walk through the entire text, with Aristotle’s own words preserved in generous quotation. The aim is to make you feel like you’ve actually read the thing — not just heard about it — while keeping the language light enough that a 2,400-year-old treatise on ontology doesn’t feel like homework. The excerpts are the point. Aristotle writes with a plainness that still works, and the best way to understand what he’s doing is to hear him do it.
One thing to know going in: this is a foundational text in the most literal sense. Aristotle isn’t arguing for controversial positions here. He’s building the scaffolding that arguments get built on — deciding what the parts of speech for reality itself look like. It’s less “here’s what I believe” and more “here’s how I think we should organize what anyone believes.” That makes it feel oddly modern, like watching someone design a database schema for the universe.
Chapter 1: Preliminary Definitions — Equivocal, Univocal, Derivative
Aristotle does something unusual for a philosopher about to build one of the most influential classification systems in history: he starts by cleaning his tools. Before he sorts all of reality into categories, he needs to sort out language itself — because the same word can mean wildly different things depending on who’s using it and why.
Imagine two people pointing at different things and both saying “animal.” One points at a living, breathing dog. The other points at a painting of a dog. Same word, totally different meanings. Aristotle calls this being named equivocally:
Things are said to be named ‘equivocally’ when, though they have a common name, the definition corresponding with the name differs for each. Thus, a real man and a figure in a picture can both lay claim to the name ‘animal’; yet these are equivocally so named, for, though they have a common name, the definition corresponding with the name differs for each.
The key test is the definition. If you asked “in what sense is this an animal?”, you’d give completely different answers for the man and the painting. The word is shared; the meaning is not.
Now contrast that with univocal naming — where the word and the definition travel together:
On the other hand, things are said to be named ‘univocally’ which have both the name and the definition answering to the name in common. A man and an ox are both ‘animal’, and these are univocally so named, inasmuch as not only the name, but also the definition, is the same in both cases: for if a man should state in what sense each is an animal, the statement in the one case would be identical with that in the other.
A man and an ox are both “animal” in the same sense — both living, sensing creatures. Ask “what do you mean by animal?” and the answer works for both. Think of it like two people holding identical keys that open the same lock.
Finally, there are derivative names — words that borrow from other words but twist the ending:
Things are said to be named ‘derivatively’, which derive their name from some other name, but differ from it in termination. Thus the grammarian derives his name from the word ‘grammar’, and the courageous man from the word ‘courage’.
A grammarian isn’t grammar — he’s the person who has grammar. The name leans on another name, like a building leaning on its foundation. Aristotle is flagging that words have family trees, and tracing those roots matters.
These three distinctions — shared name with different meanings, shared name with shared meaning, and borrowed names — are Aristotle’s way of saying: before we classify reality, let’s make sure we’re not tripped up by the slipperiness of words themselves.
Chapter 2: Forms of Speech and Predication
With his linguistic housekeeping done, Aristotle moves to the real architecture. He starts with a deceptively simple observation:
Forms of speech are either simple or composite. Examples of the latter are such expressions as ‘the man runs’, ‘the man wins’; of the former ‘man’, ‘ox’, ‘runs’, ‘wins’.
Simple expressions are lone words — “man,” “runs.” Composite expressions combine them — “the man runs.” This seems obvious, but Aristotle is laying the groundwork for something bigger: only composite expressions can be true or false. “Man” by itself isn’t true or false. “The man runs” can be checked against reality.
Now comes the heart of Chapter 2 — a fourfold classification of everything that exists, based on two questions: Can it be said of a subject? And is it present in a subject? Think of “said of” as asking whether something is a category that a thing belongs to. And “present in” as asking whether something inheres in a thing — lives inside it without being a part of it, like a quality or property.
First, things that can be said of a subject but are never present in one:
Of things themselves some are predicable of a subject, and are never present in a subject. Thus ‘man’ is predicable of the individual man, and is never present in a subject.
“Man” is a universal — you can say “Socrates is a man.” But “man” doesn’t live inside Socrates the way his particular shade of skin color does.
Aristotle pauses to clarify what he means by “present in” — and this definition is crucial:
By being ‘present in a subject’ I do not mean present as parts are present in a whole, but being incapable of existence apart from the said subject.
Imagine whiteness. It can’t just float around on its own — it needs a body to be white in. But it’s not a part of that body the way an arm is. It’s more like a guest that can never leave the hotel.
Second, things present in a subject but never said of one:
Some things, again, are present in a subject, but are never predicable of a subject. For instance, a certain point of grammatical knowledge is present in the mind, but is not predicable of any subject; or again, a certain whiteness may be present in the body (for colour requires a material basis), yet it is never predicable of anything.
This particular whiteness — not whiteness in general, but the specific whiteness of this wall — lives in the wall but can’t be said of anything else. It’s an individual quality, unrepeatable.
Third, things that are both said of a subject and present in one:
Other things, again, are both predicable of a subject and present in a subject. Thus while knowledge is present in the human mind, it is predicable of grammar.
Knowledge (the universal) is present in the mind, and it can be said of grammar — “grammar is knowledge.” It checks both boxes.
Fourth — and this is the foundation everything else will rest on — things that are neither said of a subject nor present in one:
There is, lastly, a class of things which are neither present in a subject nor predicable of a subject, such as the individual man or the individual horse. But, to speak more generally, that which is individual and has the character of a unit is never predicable of a subject.
The individual man. The individual horse. This particular being, standing right here. You can’t say it of anything else, and it doesn’t inhere in anything else. It just is. These concrete individuals are the bedrock of Aristotle’s world — the most real things there are.
Aristotle then introduces a rule about predication that chains upward like a ladder:
When one thing is predicated of another, all that which is predicable of the predicate will be predicable also of the subject. Thus, ‘man’ is predicated of the individual man; but ‘animal’ is predicated of ‘man’; it will, therefore, be predicable of the individual man also: for the individual man is both ‘man’ and ‘animal’.
If Socrates is a man, and man is an animal, then Socrates is an animal. Predication is transitive — it flows down the chain. Think of it like inheritance in a family: what’s true of the grandfather is true of the grandson.
He closes the chapter with a subtle but important point about how different classification systems have different kinds of divisions:
If genera are different and co-ordinate, their differentiae are themselves different in kind. Take as an instance the genus ‘animal’ and the genus ‘knowledge’. ‘With feet’, ‘two-footed’, ‘winged’, ‘aquatic’, are differentiae of ‘animal’; the species of knowledge are not distinguished by the same differentiae. One species of knowledge does not differ from another in being ‘two-footed’.
You don’t divide types of knowledge by asking “does it have wings?” — that’s for dividing animals. Each genus has its own set of relevant differences. But there’s a caveat:
But where one genus is subordinate to another, there is nothing to prevent their having the same differentiae: for the greater class is predicated of the lesser, so that all the differentiae of the predicate will be differentiae also of the subject.
If one genus sits inside another — like “mammal” inside “animal” — then the parent’s ways of dividing can apply to the child too. The ladder of predication works for differences, not just names.
Chapter 3: The Ten Categories
And now — the list. One of the most famous passages in the history of philosophy, delivered with Aristotle’s characteristic matter-of-factness, as if he’s reading off a grocery receipt rather than carving reality at its joints:
Expressions which are in no way composite signify substance, quantity, quality, relation, place, time, position, state, action, or affection.
Ten categories. Ten fundamental ways a simple, uncomposed word can mean something about the world. Every single thing you can say about anything falls — Aristotle claims — into one of these ten buckets.
He immediately gives examples, and they’re wonderfully concrete and grounded in the everyday Athens around him:
To sketch my meaning roughly, examples of substance are ‘man’ or ‘the horse’, of quantity, such terms as ‘two cubits long’ or ‘three cubits long’, of quality, such attributes as ‘white’, ‘grammatical’. ‘Double’, ‘half’, ‘greater’, fall under the category of relation; ‘in the market place’, ‘in the Lyceum’, under that of place; ‘yesterday’, ‘last year’, under that of time. ‘Lying’, ‘sitting’, are terms indicating position, ‘shod’, ‘armed’, state; ‘to lance’, ‘to cauterize’, action; ‘to be lanced’, ‘to be cauterized’, affection.
Imagine walking through the Lyceum — Aristotle’s own school — and pointing at things. There’s a man (substance). He’s two cubits tall (quantity). He’s white-haired (quality). He’s greater than his student (relation). He’s in the Lyceum (place). It’s yesterday’s lecture being discussed (time). He’s sitting (position). He’s armed with a stylus (state). He’s writing (action). He’s being questioned (affection — the passive counterpart to action, being acted upon).
What’s remarkable is the ambition. Aristotle isn’t categorizing just objects, or just properties, or just actions. He’s categorizing everything that language can express about the world in its simplest, uncomposed form. Substance is the anchor — the thing that exists. The other nine are ways of describing, measuring, locating, and relating that thing.
This list will dominate Western thought for two thousand years. Medieval scholars, Islamic philosophers, and modern logicians will all wrestle with it — debating whether these ten are truly exhaustive, whether some can be collapsed into others, whether Aristotle was carving nature or just mapping Greek grammar. But the audacity of the attempt is the point: one list, ten entries, all of reality sorted.
Chapter 4: Substance
This is the chapter where Aristotle plants his flag. Of the ten categories he’s laid out, substance gets the most ink — and for good reason. Everything else in the system leans on it. Without substance, there’s nothing for qualities, quantities, or relations to attach to. Think of it like a coatrack: you can hang all sorts of things on it, but without the rack itself, your coats are on the floor.
Aristotle opens with a definition that’s deceptively simple:
Substance, in the truest and primary and most definite sense of the word, is that which is neither predicable of a subject nor present in a subject; for instance, the individual man or horse.
So the individual — this particular person standing in front of you, that specific horse in the field — is substance in its purest form. Not “humanity” in the abstract. Not “horseness.” The actual, concrete thing you can point at. Aristotle calls these primary substances.
But he’s not done. There’s a second tier:
But in a secondary sense those things are called substances within which, as species, the primary substances are included; also those which, as genera, include the species. For instance, the individual man is included in the species ‘man’, and the genus to which the species belongs is ‘animal’; these, therefore — that is to say, the species ‘man’ and the genus ‘animal’ — are termed secondary substances.
Imagine a set of nesting boxes. The individual man sits inside the species “man,” which sits inside the genus “animal.” The individual is primary substance. The species and genus are secondary substances — real enough to earn the name, but one step removed from the concrete.
Why Primary Substance Is King
Aristotle is emphatic about where the weight falls. Primary substances aren’t just one kind of substance among others — they’re the foundation the entire system stands on:
Everything except primary substances is either predicable of a primary substance or present in a primary substance.
He walks through this carefully. “Animal” is predicated of the species “man,” which is predicated of the individual man. Color is present in body, which means present in individual bodies. Pull the individual out from under it all, and the whole structure collapses:
If these last did not exist, it would be impossible for anything else to exist.
That’s a striking claim. Aristotle is saying that without particular things — without this man, that horse — there would be nothing for universals, qualities, or any other category to be about. The individual is the load-bearing wall.
Species vs. Genus: A Ranking Within the Ranks
Even among secondary substances, not all are created equal. Aristotle argues that the species is “more truly substance” than the genus, and his reasoning is pleasantly practical:
For if any one should render an account of what a primary substance is, he would render a more instructive account, and one more proper to the subject, by stating the species than by stating the genus. Thus, he would give a more instructive account of an individual man by stating that he was man than by stating that he was animal, for the former description is peculiar to the individual in a greater degree, while the latter is too general.
Think of it like giving directions. If someone asks “What’s that?” and you say “an animal,” you’ve told them something — but not much. Say “a man” and you’ve told them considerably more. The species sits closer to the individual, captures more of what makes it this thing. The genus is too wide a net.
He shores this up with a structural argument too: species relates to genus the way subject relates to predicate. You can say “a man is an animal,” but you can’t turn it around and say “an animal is a man.” That asymmetry mirrors the relationship between primary substance and everything else, giving species a stronger claim to the title.
But within the same level, there’s no further ranking:
Of species themselves, except in the case of such as are genera, no one is more truly substance than another. We should not give a more appropriate account of the individual man by stating the species to which he belonged, than we should of an individual horse by adopting the same method of definition. In the same way, of primary substances, no one is more truly substance than another; an individual man is not more truly substance than an individual ox.
No hierarchy among equals. Your pet cat is exactly as much a substance as Socrates.
The Marks of Substance
Having established what substance is, Aristotle spends the back half of the chapter identifying its distinctive features — the things that set substance apart from everything else.
First mark: never present in a subject. This one applies to all substance, primary and secondary:
It is a common characteristic of all substance that it is never present in a subject. For primary substance is neither present in a subject nor predicated of a subject; while, with regard to secondary substances, it is clear from the following arguments that they are not present in a subject. For ‘man’ is predicated of the individual man, but is not present in any subject: for manhood is not present in the individual man.
This might sound odd at first — isn’t manhood present in a man? But remember Aristotle’s technical meaning of “present in a subject” from Chapter 2. Whiteness is in a body the way a quality inheres in something. But “man” isn’t in the individual man that way — it’s what the individual man is. The definition of “man” applies to the individual man, and that’s the giveaway:
Yet of secondary substances, not only the name, but also the definition, applies to the subject: we should use both the definition of the species and that of the genus with reference to the individual man. Thus substance cannot be present in a subject.
Second mark: no contrary. Substance has no opposite:
What could be the contrary of any primary substance, such as the individual man or animal? It has none. Nor can the species or the genus have a contrary.
There’s no anti-man, no opposite of horse. Aristotle is honest that this isn’t unique to substance — quantities like “two cubits long” or “ten” don’t have contraries either. But it’s still a mark worth noting.
Third mark: no variation of degree. A substance can’t be more or less itself:
One man cannot be more man than another, as that which is white may be more or less white than some other white object, or as that which is beautiful may be more or less beautiful than some other beautiful object.
White things come in degrees — this wall is whiter than that one. But a man can’t be more man than another man. Substance doesn’t do gradients:
A man is not more truly a man at one time than he was before, nor is anything, if it is substance, more or less what it is.
The Most Distinctive Mark
Now Aristotle arrives at what he considers substance’s signature feature — the thing that truly belongs to substance and nothing else:
The most distinctive mark of substance appears to be that, while remaining numerically one and the same, it is capable of admitting contrary qualities.
Think of it like a canvas that can hold entirely different paintings at different times while remaining the same canvas. A single person can be warm, then cold. White, then tanned. Healthy, then sick. The person stays numerically one — the same individual — while taking on opposite qualities at different times:
The same individual person is at one time white, at another black, at one time warm, at another cold, at one time good, at another bad.
Nothing else can do this. A color can’t be both white and black. An action can’t be both good and bad. But a substance can shuttle between contraries while remaining itself.
The Statements Exception (And Why Aristotle Rejects It)
There’s one apparent counterexample, and Aristotle deals with it head-on. Statements and opinions seem to admit contrary qualities too:
The same statement, it is agreed, can be both true and false. For if the statement ‘he is sitting’ is true, yet, when the person in question has risen, the same statement will be false.
So doesn’t that give statements the same power as substances? Aristotle says no — and his reason is precise. The difference lies in how the change happens:
It is by themselves changing that substances admit contrary qualities. It is thus that that which was hot becomes cold, for it has entered into a different state. Similarly that which was white becomes black, and that which was bad good, by a process of change.
The substance itself changes. It undergoes a real transformation. But statements?
Statements and opinions themselves remain unaltered in all respects: it is by the alteration in the facts of the case that the contrary quality comes to be theirs. The statement ‘he is sitting’ remains unaltered, but it is at one time true, at another false, according to circumstances.
The statement “he is sitting” doesn’t change at all. The man changes — he stands up — and the statement passively becomes false. The truth or falsity of a statement depends entirely on the facts, not on anything the statement does:
The truth or falsity of a statement depends on facts, and not on any power on the part of the statement itself of admitting contrary qualities. In short, there is nothing which can alter the nature of statements and opinions. As, then, no change takes place in themselves, these cannot be said to be capable of admitting contrary qualities.
Substances earn their contrary qualities the hard way — by actually changing. Statements just sit there while the world moves around them. That’s the difference, and it’s what makes substance unique.
Aristotle closes with a clean summary:
To sum up, it is a distinctive mark of substance, that, while remaining numerically one and the same, it is capable of admitting contrary qualities, the modification taking place through a change in the substance itself.
And with that, the foundation is laid. Everything else in the Categories — quantity, quality, relation, all the rest — will be understood in relation to substance. It’s the ground floor of Aristotle’s metaphysics, and he’s just spent an entire chapter making sure we know it.
Chapter 5: Quantity
Aristotle opens with a clean fork in the road. All quantity, he says, is either discrete or continuous — and the test for which is which turns out to be surprisingly elegant.
Quantity is either discrete or continuous. Moreover, some quantities are such that each part of the whole has a relative position to the other parts: others have within them no such relation of part to part.
Think of it like building blocks versus clay. Discrete quantities are the blocks — they sit next to each other but never actually merge. Continuous quantities are the clay — you can always find a seam where two parts share a boundary, fused together.
His examples for each side:
Instances of discrete quantities are number and speech; of continuous, lines, surfaces, solids, and, besides these, time and place.
The Common Boundary Test
The way Aristotle distinguishes discrete from continuous is almost tactile. Take number. You can split ten into two fives, or into three and seven, but those parts never touch:
In the case of the parts of a number, there is no common boundary at which they join. For example: two fives make ten, but the two fives have no common boundary, but are separate; the parts three and seven also do not join at any boundary.
Speech works the same way — syllables are measured (long and short), but each syllable is its own island:
It is a discrete quantity for its parts have no common boundary. There is no common boundary at which the syllables join, but each is separate and distinct from the rest.
Now flip to continuous quantities. A line is continuous because you can always point to where its parts meet — literally point to it:
A line, on the other hand, is a continuous quantity, for it is possible to find a common boundary at which its parts join. In the case of the line, this common boundary is the point; in the case of the plane, it is the line: for the parts of the plane have also a common boundary.
Notice the nesting: a point is the boundary of a line, a line is the boundary of a plane, a line or plane is the boundary of a solid. It’s boundaries all the way down — or rather, all the way up in dimension.
Time and space get folded in through an ingenious argument. The parts of a solid occupy space, and since the solid’s parts share boundaries, the parts of space they occupy must share those same boundaries. Therefore space is continuous. Time, similarly — past, present, and future form a continuous whole.
Position vs. Order
Aristotle then draws a second distinction that cuts across the first. Some quantities have parts with relative position — you can say where each part sits and what it’s next to. Others have parts with only relative order.
Lines, planes, solids, and space all have position. You can point to a segment of a line and say “this part is here, adjacent to that part.” But number? You can’t point to where the “three” in “ten” sits. And time is even more slippery:
Nor could this be done in the case of time, for none of the parts of time has an abiding existence, and that which does not abide can hardly have position. It would be better to say that such parts had a relative order, in virtue of one being prior to another.
“That which does not abide can hardly have position” — a line worth sitting with. Time has sequence (one comes before two, yesterday before today) but not location. Speech is the same: once a syllable is spoken, it’s gone.
Quantities Properly So Called
Aristotle is careful to distinguish the real thing from borrowed labels. Lines, surfaces, solids, time, place, number, speech — these are quantities in their own right. Everything else that gets called “large” or “long” is just borrowing the term:
We speak of what is white as large, because the surface over which the white extends is large; we speak of an action or a process as lengthy, because the time covered is long; these things cannot in their own right claim the quantitative epithet.
When you say a war was “long,” you really mean the time it took was long. When you say a patch of white is “large,” you mean the surface it covers is large. The war and the whiteness aren’t quantities themselves — they’re piggy-backing on ones that are.
No Contraries, No Degrees
Two properties that quantity conspicuously lacks. First, quantities have no opposites. There’s nothing that is the contrary of “two cubits long.” You might think “much” and “little” or “great” and “small” are contraries of quantity — but Aristotle springs a trap:
These are not quantitative, but relative; things are not great or small absolutely, they are so called rather as the result of an act of comparison. For instance, a mountain is called small, a grain large, in virtue of the fact that the latter is greater than others of its kind, the former less.
A mountain called small, a grain called large — the same thing can be both at once depending on what you compare it to. And if “great” and “small” were genuine contraries, something being both at the same time would violate the rule (established in the chapter on substance) that nothing admits contrary qualities simultaneously. The logic tightens further:
If ‘great’ is the contrary of ‘small’, and the same thing is both great and small at the same time, then ‘small’ or ‘great’ is the contrary of itself. But this is impossible.
Second, quantity doesn’t come in degrees. Three is not “more truly three” than another three. Two cubits long is not “more two-cubits-long” than another two cubits long. Quantities are what they are — no shading, no gradation.
The Distinctive Mark: Equal and Unequal
Every category in Aristotle gets its own signature property, and for quantity it’s this:
The most distinctive mark of quantity is that equality and inequality are predicated of it. Each of the aforesaid quantities is said to be equal or unequal.
Solids can be equal or unequal. Numbers can be equal or unequal. Time periods can be equal or unequal. But qualities like whiteness? Those aren’t equal or unequal — they’re similar or dissimilar. That’s how you know you’ve crossed from one category into another. Equality is quantity’s passport stamp.
Chapter 6: Relation
Everything so far — substance, quantity — has been about things that stand on their own. Now Aristotle turns to things that only make sense when you point at something else. Welcome to the world of relatives, where nothing exists in isolation and every concept comes with a built-in dance partner.
The setup is deceptively simple. Something is “relative” when it can only be explained by reference to another thing:
Those things are called relative, which, being either said to be of something else or related to something else, are explained by reference to that other thing. For instance, the word ‘superior’ is explained by reference to something else, for it is superiority over something else that is meant. Similarly, the expression ‘double’ has this external reference, for it is the double of something else that is meant.
“Double” means nothing on its own. Double of what? “Superior” is a word shaped like a finger pointing outward. And it’s not just the obvious mathematical pairs — habit, knowledge, perception, even physical attitude all belong here. A habit is always a habit of something. Knowledge is always knowledge of something. Strip away the “of” and you strip away the meaning.
Even something as mundane as sitting down turns out to be relative, in a roundabout way. Sitting itself isn’t relative — but “attitude” is, and sitting is a kind of attitude. The relative-ness trickles down from the category to the instance.
Contraries and Degrees
Some relatives come with built-in opposites: virtue and vice, knowledge and ignorance. But not all — “double” and “triple” have no contrary. You can’t have an anti-double. Similarly, some relatives admit of more and less (“more similar,” “less equal”), while others are fixed. Nothing is “more double” than something else. It either is or it isn’t.
The Correlative Dance
Here’s where things get interesting. Every relative has a correlative — the thing on the other end of the rope. Slave implies master, double implies half, greater implies less. These pairs are locked together:
All relatives have correlatives: by the term ‘slave’ we mean the slave of a master, by the term ‘master’, the master of a slave; by ‘double’, the double of its half; by ‘half’, the half of its double; by ‘greater’, greater than that which is less; by ‘less’, less than that which is greater.
The rule is strict: if you name a relative correctly, the correlation must work both ways.
The Wing Problem
Suppose you say a wing is relative to a bird. Sounds reasonable. But watch what happens when you try to reverse it:
If a man states that a wing is necessarily relative to a bird, the connexion between these two will not be reciprocal, for it will not be possible to say that a bird is a bird by reason of its wings. The reason is that the original statement was inaccurate, for the wing is not said to be relative to the bird qua bird, since many creatures besides birds have wings, but qua winged creature. If, then, the statement is made accurate, the connexion will be reciprocal, for we can speak of a wing, having reference necessarily to a winged creature, and of a winged creature as being such because of its wings.
The mistake is subtle but devastating. A wing isn’t relative to bird — it’s relative to winged creature. Plenty of things that aren’t birds have wings. Bats. Insects. Once you correct the correlative, the reciprocity clicks into place: a wing belongs to something winged, and something winged is winged because of its wings. Perfect symmetry.
The Rudder Problem (and How to Solve It by Making Up Words)
The wing example at least has a natural-language fix. But sometimes the right word simply doesn’t exist, and Aristotle — the father of formal logic — suggests you just invent one:
If we define a rudder as necessarily having reference to a boat, our definition will not be appropriate, for the rudder does not have this reference to a boat qua boat, as there are boats which have no rudders. Thus we cannot use the terms reciprocally, for the word ‘boat’ cannot be said to find its explanation in the word ‘rudder’. As there is no existing word, our definition would perhaps be more accurate if we coined some word like ‘ruddered’ as the correlative of ‘rudder’. If we express ourselves thus accurately, at any rate the terms are reciprocally connected, for the ‘ruddered’ thing is ‘ruddered’ in virtue of its rudder.
“Ruddered.” It’s clunky, it’s made up, and it’s perfectly logical. A rudder belongs to a ruddered thing. A ruddered thing is ruddered because of its rudder. The same trick works for heads: a head isn’t the head of an animal (plenty of animals don’t have heads), but the head of a “headed” thing.
The deeper point is methodological. Language is messier than logic. When language fails to provide the right word, the philosopher’s job is to build one — because the logical structure is there whether or not the vocabulary has caught up:
Thus we may perhaps most easily comprehend that to which a thing is related, when a name does not exist, if, from that which has a name, we derive a new name, and apply it to that with which the first is reciprocally connected.
The Stripping Test
Aristotle offers a beautifully clean test for whether you’ve identified the right correlative. Take your relative, and start stripping away all the irrelevant attributes of its correlative. If the relationship survives the stripping, you’ve named it correctly:
If the correlative of ‘the slave’ is said to be ‘the master’, then, though all irrelevant attributes of the said ‘master’, such as ‘biped’, ‘receptive of knowledge’, ‘human’, should be removed, and the attribute ‘master’ alone left, the stated correlation existing between him and the slave will remain the same, for it is of a master that a slave is said to be the slave.
But if you said the slave’s correlative is “the man,” then stripping away the attribute “master” from “the man” destroys the whole relationship. No master, no slave. The wrong name collapses under scrutiny; the right name holds.
Do Correlatives Come Into Existence Together?
Usually, yes. Double and half spring into existence simultaneously — you can’t have one without the other. Master and slave, same thing. But Aristotle spots a beautiful exception: knowledge and its object.
The object of knowledge would appear to exist before knowledge itself, for it is usually the case that we acquire knowledge of objects already existing; it would be difficult, if not impossible, to find a branch of knowledge the beginning of the existence of which was contemporaneous with that of its object.
The squaring of the circle — whether or not it’s possible — exists as a potential object of knowledge right now, even though nobody yet possesses that knowledge. And the asymmetry goes deeper:
Again, while the object of knowledge, if it ceases to exist, cancels at the same time the knowledge which was its correlative, the converse of this is not true. It is true that if the object of knowledge does not exist there can be no knowledge: for there will no longer be anything to know. Yet it is equally true that, if knowledge of a certain object does not exist, the object may nevertheless quite well exist.
If every animal disappeared tomorrow, perception would vanish — no perceivers, no perception. But the objects of perception (fire, water, heat, sweetness) would carry on perfectly well without anyone around to perceive them. The world doesn’t need an audience.
Is Any Substance Relative?
This is the chapter’s sharpest question, and Aristotle handles it with unusual caution. At first glance, things like “head” and “hand” seem relative — a head is always the head of something. But primary substances (this particular person, this particular ox) are clearly not relative. And even secondary substances like “man” or “ox” aren’t defined by reference to something external.
The worry is about parts. A head, a hand — aren’t these defined by what they belong to?
Indeed, if our definition of that which is relative was complete, it is very difficult, if not impossible, to prove that no substance is relative. If, however, our definition was not complete, if those things only are properly called relative in the case of which relation to an external object is a necessary condition of existence, perhaps some explanation of the dilemma may be found.
Aristotle’s resolution is elegant. There’s a difference between “can be explained with reference to something else” (a loose definition that would let substance in) and “can only exist in relation to something else” (a strict definition that keeps substance out). A head can be described as “the head of so-and-so,” but its existence doesn’t depend on that reference. You can know exactly what a head is — its essential character — without knowing whose head it is:
Now the head, the hand, and such things are substances, and it is possible to know their essential character definitely, but it does not necessarily follow that we should know that to which they are related.
And that clinches it. With true relatives, knowing the thing means knowing what it’s relative to — knowing “double” means knowing double-of-what. But you can know perfectly well what a head is without knowing whose head you’re looking at. So no, substance is not relative. The boundary between the categories holds.
Chapter 7: Quality
This is the longest and richest section of the Categories, and for good reason. Quality is where Aristotle meets the everyday world — the sweetness of honey, the blush of shame, the shape of a triangle. He’s trying to sort through something enormous: all the ways we describe what things are like. His answer is a four-part taxonomy that’s both surprisingly tidy and full of delightful edge cases.
The Four Kinds
First: Habits and Dispositions. This is the distinction between what sticks and what doesn’t. Knowledge and virtue are habits — once you’ve really learned something, it lodges in the mind and resists eviction. As Aristotle puts it, “knowledge, even when acquired only in a moderate degree, is, it is agreed, abiding in its character and difficult to displace, unless some great mental upheaval takes place, through disease or any such cause.” Justice, self-restraint — these are habits too. They don’t just drift away on a Tuesday afternoon.
A disposition, by contrast, is a guest that doesn’t unpack its bags. “Heat, cold, disease, health, and so on are dispositions. For a man is disposed in one way or another with reference to these, but quickly changes, becoming cold instead of warm, ill instead of well.” Think of it like the difference between knowing how to swim and feeling warm. One stays with you through winter; the other vanishes the moment you step into the shade.
But here’s the wrinkle — and Aristotle loves a good wrinkle. A disposition that overstays its welcome long enough essentially becomes a habit. “Unless through lapse of time a disposition has itself become inveterate and almost impossible to dislodge: in which case we should perhaps go so far as to call it a habit.” The boundary isn’t a wall. It’s a gradient. And there’s a neat logical asymmetry: “Habits are at the same time dispositions, but dispositions are not necessarily habits.” Every habit is also a disposition, but not every disposition earns the title of habit. All squares are rectangles, but not vice versa.
Second: Natural Capacity and Incapacity. This is about what you’re born with — not what you’ve trained, but what you came equipped to do. “We call men good boxers or runners, or healthy or sickly: in fact it includes all those terms which refer to inborn capacity or incapacity.” The good boxer isn’t good because he drilled — that would be a disposition. He’s good because his body was built for it, because he has “an inborn capacity to accomplish something with ease.”
Health lands here too: “Men are called healthy in virtue of the inborn capacity of easy resistance to those unhealthy influences that may ordinarily arise; unhealthy, in virtue of the lack of this capacity.” Even hardness and softness follow this logic — hard things resist disintegration, soft things can’t. It’s about what something is equipped to withstand by its nature, not by its training.
Third: Affective Qualities and Affections. This is the longest and most subtle of the four, and it contains one of Aristotle’s best thought experiments.
Sweetness, bitterness, heat, cold, whiteness, blackness — these are affective qualities. “Honey is called sweet because it contains sweetness; the body is called white because it contains whiteness.” Simple enough. But why “affective”? Not because the things possessing them are affected — honey isn’t undergoing something by being sweet. Rather, these qualities produce effects in us. “Sweetness has the power of affecting the sense of taste; heat, that of touch; and so it is with the rest of these qualities.” They’re called affective because they do something to our perception.
Then comes the blushing problem — Aristotle’s most vivid example in the entire treatise. Colours like whiteness and blackness are affective qualities, but for a different reason: they’re often the result of an affection. “When a man is ashamed, he blushes; when he is afraid, he becomes pale, and so on.”
Now here’s where Aristotle turns genuinely sharp. Imagine someone who blushes easily — not from a momentary embarrassment, but because their constitution just tends that way. “When a man is by nature liable to such affections, arising from some concomitance of elements in his constitution, it is a probable inference that he has the corresponding complexion of skin.” The same bodily arrangement that produced the blush of shame in one fleeting moment might be someone else’s permanent wiring. If the pallor or ruddiness “come about through long disease or sunburn, and are difficult to remove, or indeed remain throughout life,” they count as qualities — because they define what kind of person you are.
But the temporary blush? That’s just an affection, not a quality. And Aristotle draws the line with surgical precision: “The man who blushes through shame is not said to be a constitutional blusher, nor is the man who becomes pale through fear said to be constitutionally pale. He is said rather to have been affected.”
The same logic applies to the soul. Inborn irascibility or insanity — these are qualities. “People are said to be mad or irascible in virtue of these.” But the man who loses his temper when provoked? “He is not even spoken of as a bad-tempered man, when in such circumstances he loses his temper somewhat, but rather is said to be affected.” The question is always: does this condition define you, or did it merely visit you?
Fourth: Figure and Shape. The most straightforward category. “Because it is triangular or quadrangular a thing is said to have a specific character, or again because it is straight or curved; in fact a thing’s shape in every case gives rise to a qualification of it.”
Aristotle pauses to note that roughness, smoothness, density, and rarity look like qualities but aren’t — they’re really about the relative arrangement of parts. “A thing is dense, owing to the fact that its parts are closely combined with one another; rare, because there are interstices between the parts; smooth, because its parts lie, so to speak, evenly; rough, because some parts project beyond others.” These are sneakily relational, not truly qualitative.
The Properties of Quality
With his four kinds laid out, Aristotle turns to what quality does — its logical behaviour.
Contraries. Some qualities have opposites: “justice is the contrary of injustice, whiteness of blackness.” But not all. “Red, yellow, and such colours, though qualities, have no contraries.” There’s no anti-red.
Variation of degree. Most qualities admit of more and less. “Whiteness is predicated of one thing in a greater or less degree than of another.” You can become whiter, more just. But shapes refuse to play along: “Those things to which the definition of the triangle or circle is applicable are all equally triangular or circular.” You can’t be more triangular than a triangle. Either the definition fits or it doesn’t. This is a genuinely interesting asymmetry — some qualities are binary, others exist on a spectrum.
There’s also a philosophical dispute Aristotle flags without fully resolving: can justice itself admit of degree, or do people merely possess justice in varying degrees? “There are some, indeed, who dispute the possibility of variation here. They maintain that justice and health cannot very well admit of variation of degree themselves, but that people vary in the degree in which they possess these qualities.” He lets the question breathe.
The distinctive mark. Every category needs its signature property — the thing only it can do. For quality, that mark is likeness and unlikeness. “One thing is like another only with reference to that in virtue of which it is such and such; thus this forms the peculiar mark of quality.” Two things are similar because they share a quality. You’d never say two things are “alike” because they share a quantity or a location. Likeness belongs to quality alone.
The Genus Problem
Aristotle anticipates one last objection and handles it with characteristic calm. Haven’t we been talking about habits and dispositions as though they’re qualities — but didn’t we already say they were relatives? Knowledge is “knowledge of something,” which sounds relational. True, he concedes, but only at the level of the genus. “Knowledge, as a genus, is explained by reference to something else, for we mean a knowledge of something. But particular branches of knowledge are not thus explained. The knowledge of grammar is not relative to anything external, nor is the knowledge of music.”
The genus knowledge is relative. But grammar, music, boxing — these individual branches are qualities. “It is because we possess these individual branches of knowledge that we are said to be such and such.” And if something happens to fall under both quality and relation? “There would be nothing extraordinary in classing it under both these heads.” Categories, for Aristotle, aren’t jealous. They can share.
Chapter 8: Action, Affection, and the Remaining Categories
After the careful, extended treatment of quality, Aristotle wraps up the remaining categories in what amounts to a philosophical shrug. Action and affection — doing things and having things done to you — behave predictably. They admit contraries (heating versus cooling, being glad versus being vexed) and they admit degrees (you can heat something more or less). Two paragraphs. Done.
The categories of position, time, place, and state get even less ceremony. Position was already handled under relation. And as for the rest:
“As for the rest, time, place, state, since they are easily intelligible, I say no more about them than was said at the beginning, that in the category of state are included such states as ‘shod’, ‘armed’, in that of place ‘in the Lyceum’ and so on, as was explained before.”
That’s Aristotle telling you he has bigger fish to fry. The ten categories took up the first eight chapters. Now comes the real show.
Chapter 9: Opposites
With the categories catalogued, Aristotle pivots to a question that will occupy him for the rest of the work: how do things stand against each other? What does it mean for two things to be “opposite”? His answer is that there are exactly four kinds of opposition — and they behave in fundamentally different ways.
“Things are said to be opposed in four senses: (i) as correlatives to one another, (ii) as contraries to one another, (iii) as privatives to positives, (iv) as affirmatives to negatives.”
Think of it as a spectrum from the gentlest kind of opposition to the hardest. Correlatives lean on each other. Contraries push away from each other. Privation is something lost. And affirmation versus negation is the only case where logic demands a winner.
Correlatives: Opposition as Partnership
The first type barely feels like opposition at all. Double and half. Knowledge and the thing known. These are pairs that exist only through each other — you cannot have a “double” without something it’s the double of. The opposition is structural, not hostile. Each term is explained by reference to its partner.
“Double is a relative term, for that which is double is explained as the double of something. Knowledge, again, is the opposite of the thing known, in the same sense; and the thing known also is explained by its relation to its opposite, knowledge.”
Remove one side and the other collapses. It’s like asking which blade of a scissors does the cutting — the question misunderstands the relationship.
Contraries: Opposition with and without a Middle Ground
Contraries are what most people think of when they hear “opposite.” Good and bad. Black and white. But Aristotle spots a crucial distinction: some contraries have intermediates and some don’t.
When there’s no middle ground, one or the other must be present. You’re either sick or healthy — there’s no third option for an animal body. A number is either odd or even. But when intermediates exist, the either/or breaks down:
“Blackness and whiteness are naturally present in the body, but it is not necessary that either the one or the other should be present in the body, inasmuch as it is not true to say that everybody must be white or black. Badness and goodness, again, are predicated of man, and of many other things, but it is not necessary that either the one quality or the other should be present in that of which they are predicated: it is not true to say that everything that may be good or bad must be either good or bad.”
Between black and white you have grey, sallow, and every other colour. Between good and bad you have that vast middle territory of the merely adequate. The intermediates are the breathing room — they’re what keep the world from being a place of pure binary switches.
And here Aristotle drops a quiet insight about the relationship between good and evil that anticipates the entire Nicomachean Ethics:
“The contrary of a good is an evil… But the contrary of an evil is sometimes a good, sometimes an evil. For defect, which is an evil, has excess for its contrary, this also being an evil, and the mean, which is a good, is equally the contrary of the one and of the other.”
Too little courage is cowardice. Too much courage is recklessness. Both are evils, and both are contraries of each other. The good — the mean — sits between two bad extremes. Most of the time evil has a good opposite, but sometimes evil simply faces another flavour of evil across the ring.
Privation and Possession: The One-Way Door
This is where things get interesting. Blindness and sight. Toothlessness and teeth. These look like contraries, but they play by different rules.
First, privation is context-sensitive. You don’t call a newborn kitten “blind” even though it can’t see — because sight isn’t natural to it yet. Privation means the absence of something that should be there:
“We do not call that toothless which has not teeth, or that blind which has not sight, but rather that which has not teeth or sight at the time when by nature it should.”
Second, privation is a one-way door. Contraries allow movement in both directions — the sick person recovers, the white thing darkens. Even moral change is reversible:
“The bad man, if he is being brought into a better way of life and thought, may make some advance, however slight, and if he should once improve, even ever so little, it is plain that he might change completely, or at any rate make very great progress; for a man becomes more and more easily moved to virtue, however small the improvement was at first.”
But privation locks behind you:
“There may be a change from possession to privation, but not from privation to possession. The man who has become blind does not regain his sight; the man who has become bald does not regain his hair; the man who has lost his teeth does not grow a new set.”
This is what separates privation from a simple contrary. Sickness and health trade places freely. But once sight is gone, it’s gone. The door only opens one way. It’s the difference between a dimmer switch and a fuse — one adjusts, the other blows.
Aristotle also carefully separates privation from correlatives. Sight is not “sight of blindness” the way double is “double of half.” There’s no reciprocal relationship, no preposition linking them as partners. Blindness is simply the privation of sight — an absence, not a counterpart.
Affirmation and Negation: The Only Real Binary
The fourth type of opposition is the sharpest and cleanest. “He sits” versus “he does not sit.” And here, for the first time, truth and falsehood enter the picture.
“Statements opposed as affirmation and negation belong manifestly to a class which is distinct, for in this case, and in this case only, it is necessary for the one opposite to be true and the other false.”
This is the law of excluded middle, stated plainly. With contraries, neither truth nor falsehood applies — “health” and “disease” are just words, not claims. With correlatives, “double” and “half” aren’t true or false either. Only when you form a proposition — a statement about the world — does the binary kick in.
And Aristotle proves this with a thought experiment that has the quiet force of a philosophical grenade. Consider the contrary statements “Socrates is ill” and “Socrates is well”:
“If Socrates exists, one will be true and the other false, but if he does not exist, both will be false; for neither ‘Socrates is ill’ nor ‘Socrates is well’ is true, if Socrates does not exist at all.”
Both false. If there’s no Socrates, there’s no illness or wellness to attribute to him. The same goes for privation and possession — if Socrates doesn’t exist, “Socrates has sight” and “Socrates is blind” are both false. But now compare with genuine affirmation and negation — “Socrates is ill” versus “Socrates is not ill”:
“For manifestly, if Socrates exists, one of the two propositions ‘Socrates is ill’, ‘Socrates is not ill’, is true, and the other false. This is likewise the case if he does not exist; for if he does not exist, to say that he is ill is false, to say that he is not ill is true.”
Dead or alive, existing or not — one of these must be true and the other false. That’s the unique power of negation. It’s not a different quality or a lost possession or a correlated partner. It’s a logical operation that carves reality into exactly two halves, every time, without exception. The other three types of opposition are features of the world. Affirmation and negation are features of logic itself.
Chapter 10: Priority and Simultaneity
Aristotle now pivots from classifying the kinds of things that exist to classifying the kinds of relations between things — starting with the deceptively simple question: what does it mean to say one thing comes “before” another?
He finds five distinct answers hiding inside that one little word.
The first is the obvious one — time:
There are four senses in which one thing can be said to be ‘prior’ to another. Primarily and most properly the term has reference to time: in this sense the word is used to indicate that one thing is older or more ancient than another, for the expressions ‘older’ and ‘more ancient’ imply greater length of time.
Fair enough. Your grandfather is prior to you. The Roman Republic is prior to the Empire. But Aristotle is already signaling something interesting by calling this only the primary sense — implying the word does real philosophical work in other registers too.
The second sense is logical dependence — the kind of priority that mathematicians and programmers would recognize instantly:
Secondly, one thing is said to be ‘prior’ to another when the sequence of their being cannot be reversed. In this sense ‘one’ is ‘prior’ to ‘two’. For if ‘two’ exists, it follows directly that ‘one’ must exist, but if ‘one’ exists, it does not follow necessarily that ‘two’ exists: thus the sequence subsisting cannot be reversed.
Think of it like a one-way door. Two requires one (you can’t have a pair without a unit), but one doesn’t require two. Wherever you find this asymmetric dependence, the independent thing is “prior.” This is priority as logical load-bearing — which thing holds up which.
Third comes order — priority within a sequence that humans have arranged:
In the third place, the term ‘prior’ is used with reference to any order, as in the case of science and of oratory. For in sciences which use demonstration there is that which is prior and that which is posterior in order; in geometry, the elements are prior to the propositions; in reading and writing, the letters of the alphabet are prior to the syllables.
You learn the alphabet before you learn words. You prove the axioms before the theorems. This isn’t about time or logical necessity — it’s about the structure of a discipline. The exordium comes before the narrative in a speech not because it must exist for the narrative to exist, but because that’s how speeches work.
Fourth — and Aristotle is almost sheepish about this one:
Besides these senses of the word, there is a fourth. That which is better and more honourable is said to have a natural priority. In common parlance men speak of those whom they honour and love as ‘coming first’ with them. This sense of the word is perhaps the most far-fetched.
Priority as honor. Your family “comes first.” The gods are “prior” to mortals. Aristotle flags this as the most stretched usage, but he catalogues it anyway — the good taxonomist doesn’t leave specimens out just because they’re awkward.
Then, having announced four senses and wrapped them up neatly, he pauses — and admits he missed one:
Yet it would seem that besides those mentioned there is yet another. For in those things, the being of each of which implies that of the other, that which is in any way the cause may reasonably be said to be by nature ‘prior’ to the effect.
This fifth sense is causal priority, and Aristotle illustrates it with a passage that would keep philosophers of language busy for two thousand years:
The fact of the being of a man carries with it the truth of the proposition that he is, and the implication is reciprocal: for if a man is, the proposition wherein we allege that he is true, and conversely, if the proposition wherein we allege that he is true, then he is. The true proposition, however, is in no way the cause of the being of the man, but the fact of the man’s being does seem somehow to be the cause of the truth of the proposition, for the truth or falsity of the proposition depends on the fact of the man’s being or not being.
The man and the true statement about the man imply each other — they’re logically mutual. But the man is still prior, because the man is the reason the statement is true, not the other way around. Reality comes before the descriptions of reality. The world makes propositions true; propositions don’t make the world exist. That “somehow” — Aristotle hedging, feeling his way — is one of the most honest moments in ancient philosophy.
With “prior” mapped, Aristotle turns to its mirror image: simultaneity. And again, the everyday word splinters into three distinct meanings.
First, the plain temporal sense:
The term ‘simultaneous’ is primarily and most appropriately applied to those things the genesis of the one of which is simultaneous with that of the other; for in such cases neither is prior or posterior to the other. Such things are said to be simultaneous in point of time.
Two things born at the same moment. Simple enough. But the second sense is the interesting one — simultaneity in nature, which means reciprocal dependence without causation:
Those things, again, are ‘simultaneous’ in point of nature, the being of each of which involves that of the other, while at the same time neither is the cause of the other’s being. This is the case with regard to the double and the half, for these are reciprocally dependent, since, if there is a double, there is also a half, and if there is a half, there is also a double, while at the same time neither is the cause of the being of the other.
Double and half are conceptual twins — you literally cannot have one without the other, and neither one created the other. They came into being together, logically joined at the hip. Compare this to the fifth sense of “prior,” where the man and the proposition also imply each other but one is still the cause. Here, there’s no asymmetry at all.
The third sense of “simultaneous” applies to species within a genus:
Those species which are distinguished one from another and opposed one to another within the same genus are said to be ‘simultaneous’ in nature. I mean those species which are distinguished each from each by one and the same method of division. Thus the ‘winged’ species is simultaneous with the ‘terrestrial’ and the ‘water’ species. These are distinguished within the same genus, and are opposed each to each, for the genus ‘animal’ has the ‘winged’, the ‘terrestrial’, and the ‘water’ species, and no one of these is prior or posterior to another.
Winged animals, land animals, water animals — all carved out of “animal” by the same knife (mode of locomotion). None is more fundamental than the others. They’re siblings, not parent and child.
But genera and species are not simultaneous — genera are prior, because the logic runs one way:
But genera are prior to species, for the sequence of their being cannot be reversed. If there is the species ‘water-animal’, there will be the genus ‘animal’, but granted the being of the genus ‘animal’, it does not follow necessarily that there will be the species ‘water-animal’.
The genus “animal” can exist without water-animals (maybe in a world with only land creatures), but water-animals can’t exist without the genus “animal.” One-way door again — the same test from the second sense of “prior.”
Chapter 11: Movement
Aristotle now turns to motion — and by “motion” he means something broader than we do. Not just objects changing location, but any kind of change at all:
There are six sorts of movement: generation, destruction, increase, diminution, alteration, and change of place.
Six kinds. Coming into being, ceasing to be, getting bigger, getting smaller, changing qualities, and moving from here to there. Most of these are obviously distinct from each other — nobody confuses being born with moving across a room.
But alteration is the tricky case. Someone might argue that alteration is really just a side effect of one of the other five — that whenever something changes its qualities, it must also be growing, shrinking, or relocating. Aristotle pushes back:
In the case of alteration it may be argued that the process necessarily implies one or other of the other five sorts of motion. This is not true, for we may say that all affections, or nearly all, produce in us an alteration which is distinct from all other sorts of motion, for that which is affected need not suffer either increase or diminution or any of the other sorts of motion. Thus alteration is a distinct sort of motion.
And he proves it with a clean geometric example:
The square, for instance, if a gnomon is applied to it, undergoes increase but not alteration, and so it is with all other figures of this sort. Alteration and increase, therefore, are distinct.
A gnomon is that L-shaped border you add around two sides of a square to produce the next larger square (think: 3x3 becomes 4x4 by wrapping an L of seven unit-squares around it). The square gets bigger, but it doesn’t change what it is — it’s still a square, still the same shape, still the same kind of thing. Increase without alteration. And conversely, something can change color or temperature without getting any bigger. The two kinds of motion are genuinely independent.
Then Aristotle maps the contraries of each type of motion:
Speaking generally, rest is the contrary of motion. But the different forms of motion have their own contraries in other forms; thus destruction is the contrary of generation, diminution of increase, rest in a place, of change of place. As for this last, change in the reverse direction would seem to be most truly its contrary; thus motion upwards is the contrary of motion downwards and vice versa.
Generation pairs with destruction (being born vs. dying). Increase pairs with diminution (growing vs. shrinking). Change of place pairs with either staying put or moving in the opposite direction. Clean pairings.
But alteration gives him trouble again:
In the case of that sort of motion which yet remains, of those that have been enumerated, it is not easy to state what is its contrary. It appears to have no contrary, unless one should define the contrary here also either as ‘rest in its quality’ or as ‘change in the direction of the contrary quality’… In this way becoming white is the contrary of becoming black; there is alteration in the contrary direction, since a change of a qualitative nature takes place.
The contrary of “becoming white” is either staying the same color or becoming black. Aristotle isn’t fully satisfied with either answer — you can feel him testing both options and leaving the question slightly open. It’s the kind of intellectual honesty that makes him worth reading twenty-four centuries later.
Chapter 12: “To Have”
The final chapter of the Categories is barely two paragraphs long, but it’s a small masterpiece of taxonomic ambition — Aristotle taking the everyday verb “to have” and showing just how many unrelated things it’s doing:
The term ‘to have’ is used in various senses. In the first place it is used with reference to habit or disposition or any other quality, for we are said to ‘have’ a piece of knowledge or a virtue. Then, again, it has reference to quantity, as, for instance, in the case of a man’s height; for he is said to ‘have’ a height of three or four cubits. It is used, moreover, with regard to apparel, a man being said to ‘have’ a coat or tunic; or in respect of something which we have on a part of ourselves, as a ring on the hand: or in respect of something which is a part of us, as hand or foot. The term refers also to content, as in the case of a vessel and wheat, or of a jar and wine; a jar is said to ‘have’ wine, and a corn-measure wheat. The expression in such cases has reference to content. Or it refers to that which has been acquired; we are said to ‘have’ a house or a field. A man is also said to ‘have’ a wife, and a wife a husband, and this appears to be the most remote meaning of the term, for by the use of it we mean simply that the husband lives with the wife.
Count them up: having a quality (knowledge, virtue), having a quantity (height), having clothing, having something on a body part (a ring), having a body part itself (a hand), having contents (the jar has wine), having property (a house), and having a spouse. Eight distinct senses hiding inside three letters.
That last one — “having” a wife or husband — Aristotle flags as the most stretched meaning of all, since it really just means living together. And he closes with characteristic modesty:
Other senses of the word might perhaps be found, but the most ordinary ones have all been enumerated.
It’s a fitting end to the Categories as a whole. The entire treatise has been doing exactly this — taking words we use without thinking and showing that each one is secretly a Swiss Army knife, with multiple blades folded inside that we deploy without noticing. “To have” is the last demonstration: even the humblest verb, examined carefully, turns out to contain a small philosophy of possession, embodiment, containment, and companionship.
Claude’s Take
The Categories is one of those texts whose influence wildly outstrips its reading experience. It’s thirty pages of a very smart man sorting things into boxes — and if that sounds dry, well, sometimes it is. Aristotle isn’t trying to dazzle here. He’s trying to build infrastructure, and infrastructure is not glamorous work.
What works, 2,400 years later: the method. Aristotle’s instinct to take a familiar word — “opposite,” “prior,” “to have” — and show that it’s actually five or six different concepts wearing the same coat is still the fundamental move in analytic philosophy. Every time a modern philosopher says “well, it depends on what you mean by X,” they’re doing what Aristotle did here first. The wing problem and the rudder problem from Chapter 6 are genuinely delightful — watching him troubleshoot his own system in real time, inventing words when language falls short, is like watching a programmer debug with admirable patience.
The chapter on substance holds up remarkably well. The idea that individual, concrete things are the most real — that universals and properties depend on them rather than the other way around — is a position that still has serious defenders. And the argument about statements versus substances (statements don’t change to become false; the world changes around them) is a clean, sharp piece of reasoning that anticipates correspondence theories of truth by two millennia.
What’s dated: the list of ten categories itself. It’s almost certainly shaped by the structure of ancient Greek more than by the structure of reality. Kant pointed this out, and he was right. “Position” and “state” as fundamental categories of being feel like artifacts of one particular language’s grammar. The post-predicaments (chapters 9-12) are stronger than the category list, ironically — the analysis of opposition types and priority is more universal, less language-bound.
Who should read it: anyone interested in the history of ideas, logic, or classification. It’s short enough to read in an afternoon, and there’s genuine pleasure in watching the first systematic thinker in Western philosophy lay down the ground rules. You won’t be transformed by it — this isn’t the Nicomachean Ethics or the Physics — but you’ll understand where an enormous amount of later philosophy gets its vocabulary and its habits of mind.
The translation by E.M. Edghill is serviceable but shows its age. Edghill writes in the stiff Victorian academic register, which occasionally makes Aristotle sound more ponderous than he is. More recent translations (Ackrill’s is the gold standard) bring out the conversational quality of the original Greek.
Claude score: 7/10. A foundational text that does exactly what it sets out to do — build the scaffolding for systematic thinking about what exists and how we talk about it. Not Aristotle’s most exciting work, not his deepest, but arguably his most structurally important. Points for ambition, clarity of method, and the sheer audacity of trying to sort all of reality into ten buckets. Points off for the dryness of some sections, the suspicion that Greek grammar is doing some of the heavy lifting, and the rushed treatment of six out of ten categories. It’s the kind of book you’re glad exists even if you wouldn’t reread it for fun.