Isagoge: Chapter 2:2 — Of the Nature of Genus and Species

Having discussed the notion of “genus” in (what I imagine were then) everyday terms, we get to the logical definition. Much of this will be familiar.

Again, in another way that is denominated genus to which the species is subject, called perhaps from the similitude of these; for such a genus is a certain principle of things under it, and seems also to comprehend all the multitude under itself. As then, genus is predicated triply, the consideration by philosophers is concerning the third, which also they explain by description, when they say that genus is that which is predicated of many things differing in species, in answer to what a thing is, e. g. animal.

Of the three senses of “genus”, this is the one used by philosophers, i.e., this is the sense used by Thomas:

  • That to which the species is subject
  • A certain principle (that is, primary cause) of the things within it
  • That which comprehends a multitude of things.

Now we begin to contrast genus with the other kinds of predicates:

For of predicates some are predicated of one thing alone, as individuals, for instance, “Socrates,” and “this man,” and “this thing;” but others are predicated of many, as genera, species, differences, properties, and accidents, predicated in common, but not peculiarly to any one.

Individuals are predicated of one thing, but genera are “predicated in common”.

Now genus is such as “animal,” species as “man,” difference as “rational,” property as “risible,” accident as “white,” “black,” “to sit.”

Porphyry evidently regards this as a sufficient example; he’s clearly taking more for granted than I had hoped. Ah, well. In any event, these represent the five predicables:

  • Genus: Man is an animal
  • Species: Socrates is a man
  • Difference: Man is the kind of animal that is rational
  • Property: All men are risible
  • Accidents: Some men are sitting

Of these, all should be familiar by now except possibly for “property”; a property is something predicable of a being that is not essential but follows necessarily from the thing’s essence. “Risible”, as used here, means “having the ability, disposition, or readiness to laugh”; the ability to laugh is natural to all men.

I find Porphyry’s examples of accidents to be interesting. A man might be sitting, or he might be standing, or what have you; his posture is accidental in that it can change. A man might also be white or black (or brown, or what have you), and this is something that doesn’t change over the course of a man’s life. It’s accidental in that different members of the species Man have different colors. To the ancients, white men and black men are the same species just as white cats and black cats are the same species.

OK, so genera are predicated of many; how do they differ from other things that are predicated of many? And first, how do genera differ from species?

From such things then, as are predicated of one thing only, genera differ in that they are predicated of many, but on the other hand, from those which are predicated of many and from species, (they differ) because those species are predicated of many things, yet not of those which differ in species, but in number only, for man being a species, is predicated of Socrates and Plato, who do not differ from each other in species, but in number, while animal being a genus is predicated of man, and ox, and horse, which differ also in species from each other, and not in number only.

Both genus and species are predicated of many; but the members of a species differ only in number, where as the members of a genus can differ only in species.

I’m not sure quite how Porphyry is using the phrase “differ only in number”. I can think of a couple of possibilities. First, he may be speaking as though all of the members of a species are numbered; second, material objects have extension, which is to say quantity, in each of three dimensions. And all material objects differ by extension, that is, by occupying different space.

OK, so how does genus differ from property?

From property, moreover, genus differs because property is predicated of one species alone of which it is the property, and of the individuals under the species, as “risible” of man alone, and of men particularly, for genus is not predicated of one species, but of many things, which are also different in species.

It seems to me that genus differs from property in that genus describes a part of a species’ essence, while property follows necessarily from the species’ essence. The definition of property as something “predicated of one species alone” strikes me as questionable; it might be the case that only man laughs, but man would continue to laugh even if some other animal were found to laugh as well. One could argue that this would define a new genus, “laughers”, “animals that laugh”; and Man would would then a species within this genus; but I think that such a scheme will ultimately collapse of its own weight. It seems far more likely to me that there are properties shared by multiple species.

OK, so how does genus differ from difference (i.e., specific difference) and from accidents in common, those accidents that are shared by many?

Besides, genus differs from difference and from accidents in common, because though differences and accidents in common are predicated of many things, different also in species, yet they are not so in reply to what a thing is, but (what kind of a thing) it is.

The distinct I used in past months was between being something and having something. A man is an animal, and a man has rationality, or whiteness. I don’t know if that’s a safe way of speaking about it or not.

For when some persons ask what that is of which these are predicated, we reply, that it is genus; but we do not assign in answer differences and accidents, since they are not predicated of a subject, as to what a thing is, but rather as to what kind of a thing it is. For in reply to the question, what kind of a thing man is, we say, that he is rational, and in answer to what kind of a thing a crow is, we say that it is black, yet rational is difference, but black is accident.

We might also say, it is species. If you point at a dog and ask “What is it?”, I’m more likely to answer “It’s a dog,” than “It’s an animal”. I don’t know whether Porphyry means to exclude species as an answer to “What is it?”; I suspect it’s simply that he’s talking about genus at the moment, rather than species.

In any event, neither difference or accident are appropriate answers to the question “What is it?”,
but only to the question, “What kind of thing is it?”

Now Porphyry sums up:

When however we are asked what man is, we answer, an animal, but animal is the genus of man, so that from genus being predicated of many, it is diverse from individuals which are predicated of one thing only, but from being predicated of things different in species, it is distinguished from such as are predicated as species or as properties. Moreover, because it is predicated in reply to what a thing is, it is distinguished from differences and from accidents commonly, which are severally predicated of what they are predicated, not in reply to what a thing is, but what kind of a thing it is, or in what manner it subsists: the description therefore of the conception of genus, which has been enunciated, contains nothing superfluous, nothing deficient.

Next, Porphyry will address species, and then the relation between genus and species.

Comments are closed.