Part I, Chapter 7: Of the Five Kinds of Universal Ideas: Genus, Species, Difference, Property, Accident
WHAT we have said in the preceding chapters enables us to render intelligible, in a few words, the five Universals, which are commonly expounded in the schools. For, when general ideas represent to us their objects, as things, and are marked by terms called substantive or absolute, they are called genera or species.
GENUS.—Those are called GENERA, which are so common that they extend to other ideas, which are yet themselves universals; as, quadrilateral is a genus in relation to parallelogram and trapezium; substance is a genus in relation to substance extended, which is called body,—and to substance that thinks, which is called mind.
SPECIES.—And those common ideas which are under one more common or general are called SPECIES; as parallelogram and trapezium are species of quadrilateral; body and mind, of substance. And thus the same idea may be a genus, when compared with other ideas to which it extends,—and a species, when compared to another which is more general. Thus body, which is a genus in relation to body animate and inanimate, is a species in relation to substance; and quadrilateral, which is a genus in relation to parallelogram and trapezium, is a species in relation to figure.
But there is another notion of the word species, which is applicable only to ideas which cannot become genera: this is the case when an idea contains under it only the individual and the singular; as circle has under it only individual circles, which are all of the same species. This is what is termed the lowest species (species infima). And there is a genus which is not a species, to wit, the highest of all genera; whether this genus be being, or whether it be substance, is a point of little consequence, and belongs more to metaphysics than to logic.
I have said that the general ideas which represent their objects to us as things, are called genera or species; for it is not necessary that the objects of these ideas be really things and substances,—it is enough that we consider them as things, inasmuch as, even where they are modes, we do not refer them to their substances, but to other ideas of mode, more or less general; as figure, which is only a mode in relation to figured body, is a genus in relation to figures curvilineal and rectilineal, &c. And, on the contrary, those ideas which represent their objects to us as things modified, and which are expressed by terms adjective or connotative, if we compare them with the substances which these connotative terms signify confusedly, though directly (whether, in truth, these connotative terms signify essential attributes, which are, in reality, only the thing itself, or whether they signify true modes), they are not then called either genera or species, but differences, properties, or accidents.
They are called differences, when the object of these ideas is an essential attribute, which distinguishes one species from another: as extended, heavy, reasonable.
They are called properties, when their object is an attribute, which belongs, indeed, to the essence of the thing, but which is not the first we consider in that essence, but only dependent on the first: as divisible, immortal, teachable.
And they are called common accidents when their object is a true mode, which may be separated, at least, by the mind, from the thing of which it is termed the accident, without destroying in our mind the idea of that thing: as round, hard, just, prudent. This it is necessary to explain more particularly.
DIFFERENCE.—When a genus has two species, the idea of each species must necessarily comprehend something which is not comprised in the idea of the genus, otherwise, if each contained only what is comprised in the genus, there would be only the genus; and, as the genus agrees with every species, every species would agree with each other. Thus the first essential attribute, that each species comprehends more than the genus, is called its DIFFERENCE, and the idea which we have of it is a universal idea, because one and the same idea may represent to us that difference wherever we find it, that is to say, in all the inferiors of the species.
Example.—Body and mind are two species of substance,—it is, therefore, necessary that there be something more in the idea of body than in that of substance, and also in that of mind. Now the first thing we see more in the body extension, and the first thing we see more in spirit is thought. Thus the difference of body will be extension, and that of mind, thought, that is to say, body will be a substance extended, and mind a substance which thinks.
Hence we may see, in the first place, that the difference has two aspects—one to the genus, which it divides and shares, another to the species, which it creates and constitutes making the chief part of that which is included in the idea of species according to its comprehension; whence it happens that all species may be expressed by a single name, as mind, body, or, by two words, viz., by that of the genus and that of its species united together. This is what is termed definition: as substance extended, substance which thinks.
We may see, in the second place, that since the difference constitutes the species, and distinguishes it from other species, it must have the same extension as the species—and thus, that we must needs be able to affirm them reciprocally of each other, as everything that thinks is mind and all that is mind, thinks.
It often, however, happens, that in certain things we do not see any attribute—such that it agrees to the whole of a species, and to nothing but that species. In this case we join several attributes together, the union of which being only found in that species, constitutes its difference. Thus the Platonists, holding the demons to be rational animals as well as man, found that the difference, rational was not convertible with man, hence they added to it another, mortal, which is not convertible with man either, since it agrees also with beasts; but the two together agree with man alone. And we proceed in the same way, in the idea which we form to ourselves of the majority of animals.
Finally, it may be remarked, that it is not always necessary that the two differences which divide a genus be both positive; it is sufficient if one be so, as two men are distinguished from one another, if one has a commission which the other has not, though he who has not the commission may have nothing which the other has not. It is thus that man is distinguished from the beasts in general, inasmuch as man is an animal endowed with a mind,—animal mente praeditum,—and that a beast is simply an animal—animal memni;—for the idea of beast, in general, involves nothing positive which may not be in man; there is only joined to it the negation of that which is in man, to wit, mind, so that all the difference which exists between the idea of animal and that of brute, is, that the idea of animal does not involve thought in its comprehension, but does not exclude it either, since it includes it in its extension; whereas, the idea of brute excludes it in its comprehension, and thus cannot agree with an animal that thinks.
PROPERTY.—When we have found the difference which constitutes a species, that is to say, its main essential attribute which distinguishes it from all other species, if, considering its nature more particularly, we discover in it some other attribute which is necessarily connected with the first, and which, consequently, agrees to the whole of that species, and to that species alone—omni et soli—we denominate it PROPERTY, and expressing it by a connotative term, we attribute it to the species as its property. And since it agrees with all the inferiors of the species, and that the single idea which we have once formed of it will represent that property wherever we may meet with it, we make it the fourth of the terms common and universal.
Example.—To have a right angle is the essential difference of a rectangular triangle; and since it follows necessarily, in relation to a right angle, that the square of the side which subtends it be equal to the squares of the two sides which contain it, the equality of these squares is regarded as the property of a rectangular triangle, which is common to all rectangular triangles, and to them alone.
The word property has, however, been sometimes extended beyond this, and four species of it have been discriminated.
The first is that which we have explained—“quod convenit omni, et soli, et semper”—as it is the property of every circle, of the circle alone, and always that the lines drawn from the centre to the circumference be equal.
The second—" quod convenit omni, sed non soli”—as we say that divisibility is the property of extension, since anything extended may be divided, although time, number, and force, may be so also.
The third is—" quod convenit soli, sed non omni”—as it belongs to man alone to be a physician or a philosopher, though all men may not be so.
The fourth—" quod convenit omni et soli, sed non semper”—an example of which is given in the changing of colour of the hair to grey—canescere—which is common to all men, and to men alone, but only in old age.
ACCIDENT.—We have already said, in the second chapter, that what is called a mode is that which can only exist naturally, by means of a substance, and which is not necessarily connected with the idea of a thing, so that we can easily conceive the thing without conceiving the mode, as we can easily conceive a man without conceiving that he is prudent; but we cannot conceive prudence without conceiving either a man or some other intelligent nature, which may be prudent.
Now, when we connect a confused and indeterminate idea of substance with a distinct idea of some mode, that idea is capable of representing anything in which the mode can exist: as the idea of prudent, all prudent men,—the idea of round, all round bodies; and then this idea, expressed by a connotative term—prudent, round—makes the fifth universal, which we call accident, since it is not essential to the thing to which it is attributed; for, if it were, it would be difference or property.
But it must be noticed here, as we before said, that when we consider two substances together, we may regard one as a mode of the other. Thus a man dressed may be considered as a whole made up of the man and his dress; but to be dressed is, in relation to the man, only a mode or phase of existence under which we regard him, although the parts of the dress may be themselves substances. And thus to be clothed is simply a fifth universal.
This is more than sufficient touching the five universals, which are treated at such length in the schools. For it is of very little consequence to know that there are genera, species, differences, properties, and accidents; the main thing is to recognise the true genera of things, the true species of each genus, their true differences, their true properties, and the accidents which may be attributed to them. On this matter we shall throw some light in the following chapter, after having, first of all, said something of complex terms.