23 On Difference
A third point of agreement is that genera and species constitue wholes. The term 'whole' here should be understood to mean 'more common'.
23: On Difference The third species of universal is difference. For the sake of clarity it should be noted, as Porphyry points out, that the term 'difference' is used in three senses.' One of these is broad, one narrow, the third still narrower.
In the very broad sense a difference is anything which is predicated of something, although not in quid, and denied of something else. In this sense the term
'difference' covers not only what is most properly called difference but also property and accident. Thus, the term is common to three different species of universals: difference, property, and accident.
In the narrow sense a difference is what is proper to one thing and cannot belong to another, or as Porphyry says a difference (in the narrow sense) is what belongs to a thing and cannot successively belong and fail to belong to that thing without the thing's ceasing to exist. In this sense 'difference' covers the inseparable accident of which I shall speak later.
In the narrower sense 'difference' refers to what is called the specific difference.
One can, however, divide the notion of difference in another way. Although this new division is not incompatible with the first, it yields four senses in which something can be a difference: a strict sense, a broad sense, a broader sense, and a broadest sense.
In the narrowest sense a difference is what is predicated of something in the first mode of perseity, but which does not signify anything extrinsic to the thing for which it supposits and of which it is predicated. In this sense,'difference' refers to one of the five universals and designates the topic to be considered in this chapter.
In a broader sense a difference is what is necessarily predicated of something, but which cannot belong to all things. In this sense it can be said that risible is a difference of man, because the proposition 'Man is risible' is necessary.
In a still broader sense a difference is what is predicated of something but cannot, as a matter of natural fact, be affirmed and denied of that thing with- [bid., chapter III (p.
On Difference out the thing ceasing to exist. In this sense an inseparable accident is a difference.
Finally, in the broadest sense a difference isany thing which is predicated of one thing, but not of all things; and in this sense even a separable accident is said to be a difference. Thus, if Socrates is white and Plato black, it can be said that white is a difference of Socrates; for while Socrates is white Plato is not.
Leaving aside for the present the last three elements in this division, let us concentrate on the first. It should be understood that a difference is not something belonging to the essence of a thing; it is an intention of the soul predicable of the things contained under it, but not in quid. Such an intention is
Said to be a difference because, although not predicable in quid, it can function as the middle term in an argument in which we conclude that the thing of which it is the difference is different from some other thing. Thus, rational is the middle term for deriving the negative proposition that man is not a donkey or something else different from man. Consider the following argument:
Every man is rational; no donkey is rational; therefore, no donkey is a man.
Thus, it should not be thought that the difference is something intrinsic to a species by which one species is distinguished from another; for then the difference would not be a universal, but would be matter, form, or the whole composed of matter and form. On the contrary the difference is a predicable proper to one species, but not another. It is called the essential difference not because it belongs to the essence ofa thing, but because it expresses part of the essence of a thing and nothing extrinsic to the thing.
The difference, as I am now using the term, always expresses a part of the thing. Some differences express the material part while others express the formal. Thus, the difference of man, rational, expresses man's intellective soul in the way that white expresses whiteness and besouled the soul. But the difference material expresses matter in the same way that besouled expresses the soul. Consequently, we must reject the view of those recent writers who say the difference is taken only from the form and not the matter; the difference can be taken from either the matter or the form. Although one difference is taken from the matter and another from the form, every difference when placed in a definition functions as form; for as the form comes to the matter and presupposes it, so in definition the difference always comes to the genus.
First we assign the genus and second the difference. The point holds regardless of whether the difference is taken from the matter or the form. Thus, body is defined as a substance having matter. We posit the genus 'substance' first and then the difference having matter. The difference in question, however, is taken from and principally designates the matter.
From the foregoing, it follows that no species which is common to simple entities (i.e., those lacking composition in terms of matter and form) has an On Difference essential difference, for an entity of that sort has no parts. It can, however, have accidental differences.
It also follows that no species which is common to simple things, whether it belongs in the category of substance or some other category, is definable by what can properly be called a definition. A species of this sort can, of course, be defined in terms of definition by addition. Therefore all the authorities who say, for example, that every genus is divided by its differences or that species have a constitutive difference can be interpreted in one of two ways. Either they are speaking only of genera and species which actually have essential differences. Thus, when they say that every genus is divided by its differences they mean that every genus which has such differences is divided by them. Or they are using the term 'difference' to cover both essential and accidental differences—in my scheme the first and third kinds of differences.
It should be pointed out that when asserted such propositions as 'The difference is that by which the species goes beyond the genus'; 'The difference is constitutive of the species'; 'The difference divides the genus into its species',
'The difference is that by which particulars differ'; and 'The difference is a part of the species', do not mean that the difference is some real entity present in the species. Rather, the difference is a predicable which is proper to something and which belongs in the definition of that thing. 'The species goes beyond the genus by its difference' means that the difference belongs in the definition of the species, but not in the definition of the genus. Similarly, 'The difference is constitutive of the species' means that the difference completes the definition of the species. In the same way, "The difference is that by which particulars differ means that the difference is proper in predication to one thing and not another and that it can function as a middle term for concluding that one thing is to be denied of another. 'The difference is part of the species' means that the difference expresses a part of the thing which is signified by the species or is a part of the definition which signifies the same thing as the species. Thus when Porphyry says that differences are potentially in the genus, he means that the difference is not predicated of the genus taken universally but particularly.'
Therefore, the difference is an intention of the soul which expresses a determinate part of a thing and which is predicable in quale of the same things that the species with which it is convertible is predicable in quid. That the difference is an intention of the soul is clear from the fact that it is a universal.
Every universal, I have shown, is an intention of the soul, unless one also wants to call conventional signs universals; but I am not now speaking of universals which are conventional; only of those which are universal by nature.
That the difference expresses a part of the thing is clear. The difference must signify something on the part of the thing. It does not signify the whole thing
! [bid. (p. 621, Owen).