Republic [Politeia, c.380 BC], 507b1–517c6. Trans. B. Jowett, in The Dialogues of Plato (Oxford: Clarendon, 1892), vol. III, pp. 207–17; with minor modifications.
2 Individual Substance: Aristotle, Categories*
Aristotle’s approach to the nature of reality is more robustly down to earth than Plato’s. He accepts the need to identify something stable and enduring in a world of constant change, but he rejects the notion of universal Forms or essences in the Platonic sense of items with a reality of their own distinct from particular instances of things. For Aristotle, the ultimate units of being are individual substances – for example a particular man, or a particular horse.
Aristotle arrives at this view by linking the concept of a substance with the grammatical notion of a subject. In the sentence ‘Bucephalus is strong’, Bucephalus (the famous warhorse of Alexander the Great) is the subject, and ‘strong’ the predicate: we may say that strength is predicated of the subject; the quality of strength is to be found in this horse. The subject, Bucephalus, by contrast, exists in its own right: it does not have to exist in something else.
In the extract that follows, Aristotle points out that ‘a substance, numerically one and the same, is able to receive contraries. For example, an individual man, one and the same, becomes pale at one time and dark at another.’ Of course, not all the properties of an individual can change: if a horse sprouted horns and chewed the cud it would cease to be a horse altogether. So in addition to the accidental or contingent properties (like being fat, or healthy, or fast or lame) that may change from day to day, or year to year, substances have essential characteristics which make them the kinds of thing they are. But these universal essences, for Aristotle, have no independent reality in their own right: they simply exist in the particular substances of which they are instances. So while Plato puts universals higher in the order of being (particular horses are but pale copies of the Form of Horse), Aristotle reverses the order: it is individual substances (like a particular horse) that exist independently; equine properties or ‘predicates’ (e.g. being a quadruped, having a mane, being strong, and so on) cannot exist independently, but only in a particular subject.
A substance – that which is called a substance most strictly, primarily and most of all – is that which is neither said of a subject nor in a subject:1 for example, the individual man, or the individual horse. The species in which the things primarily called substances are, are called secondary substances, as also are the genera of these species. For example, the individual man belongs in a species, man, and animal is a genus of the species; so these – both man and animal – are called secondary substances.
It is clear from what has been said that if something is said of a subject both its name and its definition are necessarily predicated of the subject. For example, man is said of a subject, the individual man, and the name is of course predicated (since you will be predicating man of the individual man), and also the definition of man will be predicated of the individual man (since the individual man is also a man). Thus both the name and the definition will be predicated of the subject. But as for things which are in a subject, in most cases neither the name nor the definition is predicated of the subject. In some cases there is nothing to prevent the name from being predicated of the subject, but it is impossible for the definition to be predicated. For example, white, which is in a subject (the body), is predicated of the subject; for a body is called white. But the definition of white will never be predicated of the body.
All the other things are either said of the primary substances as subjects or in them as subjects. This is clear from an examination of cases. For example, animal is predicated of man and therefore also of the individual man; for were it predicated of none of the individual men it would not be predicated of man at all. Again, colour is in body and therefore also in an individual body; for were it not in some individual body it would not be in body at all. Thus all the other things are either said of the primary substances as subjects or in them as subjects. So if the primary substances did not exist it would be impossible for any of the other things to exist.
Of the secondary substances the species is more a substance than the genus, since it is nearer to the primary substance. For if one is to say of the primary substance what it is, it will be more informative and apt to give the species than the genus. For example, it would be more informative to say of the individual man that he is a man than that he is an animal (since the one is more distinctive of the individual man while the other is more general); and more informative to say of the individual tree that it is a tree than that it is a plant. Further, it is because the primary substances are subjects for all the other things and all the other things are predicated of them or are in them, that they are called substances most of all. But as the primary substances stand to the other things, so the species stands to the genus: the species is a subject for the genus (for the genera are predicated of the species but the species are not predicated reciprocally of the genera). Hence for this reason too the species is more a substance than the genus.
But of the species themselves – those which are not genera – one is no more a substance than another: it is no more apt to say of the individual man that he is a man than to say of the individual horse that it is a horse. And similarly of the primary substances one is no more a substance than another: the individual man is no more a substance than the individual ox.
It is reasonable that, after the primary substances, their species and genera should be the only other things called (secondary) substances. For only they, of things predicated, reveal the primary substance. For if one is to say of the individual man what he is, it will be in place to give the species or the genus (though more informative to give man than animal); but to give any of the other things would be out of place – for example, to say ‘white’ or ‘runs’ or anything like that. So it is reasonable that these should be the only other things called substances. Further, it is because the primary substances are subjects for everything else that they are called substances most strictly. But as the primary substances stand to everything else, so the species and genera of the primary substances stand to all the rest: all the rest are predicated of these. For if you will call the individual man grammatical it follows that you will call both a man and an animal grammatical; and similarly in other cases.
It is a characteristic common to every substance not to be in a subject. For a primary substance is neither said of a subject nor in a subject. And as for secondary substances, it is obvious at once that they are not in a subject. For man is said of the individual man as subject but is not in a subject: man is not in the individual man. Similarly, animal also is said of the individual man as subject but animal is not in the individual man. Further, while there is nothing to prevent the name of what is in a subject from being sometimes predicated of the subject, it is impossible for the definition to be predicated. But the definition of the secondary substances, as well as the name, is predicated of the subject: you will predicate the definition of man of the individual man, and also that of animal. No substance, therefore, is in a subject.
This is not, however, peculiar to substance; the differentia also is not in a subject. For footed and two-footed are said of man as subject but are not in a subject; neither two-footed nor footed is in man. Moreover, the definition of the differentia is predicated of that of which the differentia is said. For example, if footed is said of man the definition of footed will also be predicated of man; for man is footed.
We need not be disturbed by any fear that we may be forced to say that the parts of a substance, being in a subject (the whole substance), are not substances. For when we spoke of things in a subject we did not mean things belonging in something as parts.
It is a characteristic of substances and differentiae that all things called from them are so called synonymously. For all the predicates from them are predicated either of the individuals or of the species. (For from a primary substance there is no predicate, since it is said
