Once he has finished the preliminary teaching of the Categories and named the ten categories, Aristotle turns to the first of them, which is substance. He gives the whole of Chapter 5 to it. The chapter opens with two paragraphs. The first defines primary substance and the second names the secondary substances. Following the commentary of St. Albert the Great, this article explains four things: the sense in which the logician uses the word “substance,” which things are substances in the fullest sense, what a primary substance is and why it is called primary, and what the secondary substances are.
I. Primary Source Text
Aristotle, Categories, Chapter 5 (2a11–19)
Substance, which is most properly, primarily, and especially so called, is that which is neither predicated of any subject, nor is in any subject; such for instance as, an individual man, an individual horse.
But secondary Substances are called Species, in which Species those Substances that are named primary Substances are contained — both these, and the Genera of these Species. Thus, an individual man is contained in man as in Species; but the Genus of the Species man is animal. These, therefore, are called secondary Substances, such for instance as man and animal.
II. Exposition
The Logical and Metaphysical Senses of “Substance”
St. Albert warns that the word substance is used in more than one way, and that the reader must know which sense Aristotle intends in the Categories.
In Metaphysics, one asks which things are substances. Is a stone a substance? Is the soul a substance? These questions concern things themselves, not ideas or words. St. Albert assigns them to Metaphysics, which studies what things are.
Logic does not ask which things are substances. It takes the word “substance” and asks how it is said of other words. If we ask what Socrates is, the answer is that he is a man. If we ask what a man is, the answer is that he is an animal. If we ask what an animal is, the answer is that it is a substance. If we ask what a substance is, there is no wider answer to give. Every word that tells what a thing is leads up to the word “substance,” but “substance” leads up to nothing. St. Albert teaches that this is how Logic considers substance, and that this is the sense Aristotle intends here.
Why the Individual Is Substance in the Fullest Sense
Before he takes up Aristotle’s first sentence, St. Albert explains which things are substances in the fullest sense.
Consider Socrates, an individual man. Socrates is a man. Socrates is white. Socrates is seated. Man is said of Socrates. White is in Socrates. Sitting is in Socrates. All of these belong to Socrates, but Socrates belongs to nothing else.
St. Albert therefore concludes that, taken in this way, only the individual is a substance. Only the individual has everything else belonging to it while it belongs to nothing. Man does not, and white does not. When we say that white is in man, we say it because individual men are white.
Aristotle’s Definition of Primary Substance
Aristotle’s first sentence defines substance “most properly, primarily and especially so called” as that which is neither said of any subject nor in any subject. His examples are an individual man and an individual horse.
This definition depends on the fourfold division of beings given earlier in the Categories (Chapter 2). A thing said of no subject is particular. A thing in no subject is a substance. A primary substance is therefore the fourth member of that division: the particular substance, said of nothing and in nothing. Socrates, an individual man, is a primary substance.
What “Said of No Subject” and “In No Subject” Reveal
St. Albert explains what each half of the definition tells us about Socrates.
Said of no subject. From this St. Albert concludes that Socrates is one real man and not a name shared by many. Man is a name shared by many, for it is said of Socrates, of Plato, and of every other man. Socrates is said of no one but Socrates.
In no subject. From this St. Albert concludes that Socrates does not need anything else to exist in, and does not get his existence from anything he is in. The whiteness of Socrates needs Socrates, but Socrates needs no such thing.
Why Primary Substance Is Defined by Negation
St. Albert also answers a question a careful student will ask: why does Aristotle say what a primary substance is not, instead of saying what it is?
The answer is that both marks are things it lacks. Socrates has nothing beneath him, so there is nothing for him to be said of. And Socrates is in nothing, because everything else is in him. A thing at the bottom of the tree, which holds up everything else, is best described by saying that it holds up all things and is held up by nothing. This is what the word “substance” means: that which stands by itself.
Substance “Most Properly, Primarily, and Especially”
Aristotle does not simply call this substance. He calls it substance most properly, primarily and especially. St. Albert gives a reason for each of the three words.
Properly. Sometimes a thing in another category is called a “substance,” but only because it does something like what a substance does. Color does for whiteness what animal does for man: it says what whiteness is. Because of this likeness, someone may call color the “substance” of whiteness. But color is not a substance at all; it is a quality. The word properly rules out this loose way of speaking.
Primarily. This word places primary substance above the secondary substances. Man and animal are called substances, but nothing belongs to man or to animal the way whiteness and sitting belong to Socrates. Man is called a substance because Socrates and the other men it is said of are substances, not because “man” is itself a substance.
Especially. Primary substance is substance especially because more belongs to it than to anything else. Man is said of Socrates, and animal is said of him. Whiteness, sitting, and the shoes he wears are also in Socrates, and they are in no one else. More belongs to Socrates than to any name above him.
III. Secondary Substances: Species and Genera
Aristotle’s second sentence names the secondary substances. They are the species that contain the primary substances, together with the genera of those species.
In Aristotle’s example, “this man” is contained in man as in its species, and the genus of the species man is animal. Man and animal are therefore secondary substances.
Secondary Substance and the Tree of Porphyry
The same order appears in the Tree of Porphyry. Substance stands at the top as the most general genus. Below it stand body, animated body, animal, and man, which is the most special species. Below man stands Socrates. Every term on the tree above Socrates is a secondary substance. Socrates himself is a primary substance.
Secondary Substance as Universal Substance
Secondary substance can also be placed within the fourfold division of Chapter 2. A secondary substance is said of a subject, for man is said of Socrates and animal is said of man. It is in no subject, for man is not in Socrates the way white is in a body. A secondary substance is therefore the first member of that division: the universal substance.
| Said of a subject? | In a subject? | Kind | |
|---|---|---|---|
| Primary substance (e.g., Socrates) | No | No | Particular substance |
| Secondary substance (e.g., man, animal) | Yes | No | Universal substance |
IV. Summary of the Doctrine
The logical sense of substance. The logician does not ask which things are substances; that question belongs to Metaphysics. He asks how the word “substance” is said of other words. Every word that tells what a thing is leads up to substance, and substance leads up to nothing higher.
Substance in the fullest sense. Everything belongs to the individual, as it does to Socrates, but the individual belongs to nothing. In this way of speaking, the individual is substance properly, primarily and especially.
Primary substance. A primary substance is neither said of any subject nor in any subject, like this individual man or this individual horse. Because it is said of no subject, it is truly an individual existing in act. Because it is in no subject, it is a being through itself.
The three words. It is substance properly because it is not called substance on account of a likeness. It is substance primarily because the secondary substances are called substances only because the individuals they are said of are substances. It is substance especially because more belongs to it than to anything else, accidents included.
Secondary substances. The secondary substances are the species that contain the primary substances, together with the genera of those species, like man and animal.
Key Concepts
- Primary substance (prima substantia): The individual existent, such as this man or this horse, which is neither said of any subject nor present in any subject.
- Secondary substance (secunda substantia): The species and genera that contain primary substances, such as man and animal, which are said of a subject but are present in no subject.
- Said of a subject: Aristotle’s mark of the universal, by which one term is predicated of many as telling what they are, as man is said of Socrates.
- In a subject: Aristotle’s mark of the accident, which cannot exist apart from that in which it is, as whiteness is in a body.
- Tree of Porphyry (Arbor Porphyriana): The ordered descent of the category of substance from the most general genus, substance, through intermediate genera to the most special species, man, and finally to the individuals beneath it.
How to Cite This Reference:
Chicago: Classical Liberal Arts Academy. “Primary and Secondary Substance in Aristotle’s Categories (TRV-362 Lesson 06).” CLAA Library, 2026. https://www.classicalliberalarts.com/aristotles-categories-primary-secondary-substance/.
MLA: Classical Liberal Arts Academy. “Primary and Secondary Substance in Aristotle’s Categories (TRV-362 Lesson 06).” CLAA Library, 2026, www.classicalliberalarts.com/aristotles-categories-primary-secondary-substance/.
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