Isagoge: Chapter 9 — Of the Community and Difference of Genus and Property

Compare and contrast. First, we’ll compare:

Both to genus and to property it is common to follow species, for if any thing be man, it is animal, and if any thing be man, it is risible. Likewise to genus, to be equally predicated of species, and to property, (to be equally predicated) of the individuals which participate it; thus man and ox are equally animal, and Anytus and Melitus risible. It is also common that genus should be univocally predicated of its proper species, and property of the things of which it is the property;

So if A is a member of a species S, then we know immediately that A is a member of the genus G to which the species belongs, and that A has all of the properties P of S. Further, not only is G predicated of all species within it, just as P is predicated of all individuals in S, but each is predicated univocally, that is, in exactly the same way. When we say that all men laugh, the term “laugh” doesn’t have different shades of meaning for different men, but it means the same thing for all men. Similarly, when we say that all men are animals, we mean it in the same way for all men.

And now we’ll contrast.

…still they differ, because genus is prior, but property posterior, for animal must first necessarily exist, afterwards be divided by differences and properties.

You can’t have a species until you have a genus, and you can’t have a property until you have a species.

Also genus indeed is predicated of many species, but property of one certain species of which it is the property.


Besides property is reciprocally predicated of that of which it is the property, but genus is not reciprocally predicated of any thing, for neither if any thing is an animal, is it a man, nor if a thing be animal is it risible, but if any thing is a man it is risible, and vice versa.

From this it is clear that Porphyry’s using the word “property” in its narrowest sense, as we saw in Chapter 4.

Moreover, property is inherent in the whole species, of which it is the property, in it alone, and always, but genus in the whole species indeed of which it is the genus, and always, yet not in it alone;


…once more, properties being subverted do not co-subvert genera, but genera being subverted, co-subvert species, to which properties belong; wherefore, also those things of which there are properties, being subverted, the properties themselves also, are co-subverted.

If being A does not have property P of species S, it might still belong to some other species of genus G. But if being A doesn’t belong to genus G, then it clearly doesn’t have property P.

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