With respect to these classes of Attributives (Differentia, Proprium, Accidens) this is necessary to be observed, and remembered; that they differ from one another only by the accident of their application. Thus, when rational, applied to the Genus animal, constitutes the Species man, all other Attributives applied to that Species are either accidens, or proprium; but these Attributives themselves may be the differentia in the case of other classes. Thus, warm-blooded, applied to man, stands under the class proprium; but 168 when applied to the animals which stand distinguished from the cold-blooded, as constituting a class, it becomes the differentia, and rational, with respect to this comprehensive class, is only an accidens.[50]
[50] The author says, that no very distinct boundaries are marked by the three terms, Differentia, Proprium, and Accidens, nor do they effect a scientific division. As used, however, by the more accurate of the school logicians, they do mark out distinct boundaries, and do effect a scientific division.
Of the attributes common to a class, some have been taken into consideration in forming the class, and are included in the signification of its name. Such, in the case of man, are rationality, and the outward form which we call the human. These attributes are its Differentiæ; the fundamental differences which distinguish that class from the others most nearly allied to it. The school logicians were contented with one Differentia, whenever one was sufficient completely to circumscribe the class. But this was an error, because one attribute may be sufficient for distinction, and yet may not exhaust the signification of the class-name. All attributes, then, which are part of that signification, are set apart as Differentiæ. Other attributes, though not included among those which constitute the class, and which are directly signified by its name, are consequences of some of those which constitute the class, and always found along with them. These attributes of the class are its Propria. Thus, to be bounded by three straight lines is the Differentia of a triangle: to have the sum of its three angles equal to two right angles, being a consequence of its Differentia, is a Proprium of it. Rationality is a Differentia of the class Man: to be able to build cities is a Proprium, being a consequence of rationality, but not, as that is, included in the meaning of the word Man. All other attributes of the class, which are neither included in the meaning of the name, nor are consequences of any which are included, are Accidents, however universally and constantly they may be true of the class; as blackness, of crows.
The author’s remark, that these three classes of Attributives differ from one another only in the accident of their application, is most just. There are not some attributes which are always Differentiæ, and others which are always Propria, or always Accidents. The same attribute which is a Differentia of one genus or species, may be, and often is, a Proprium or an Accidens of others, and so on.—Ed.
169 We now arrive at a very important conclusion; for it thus appears, that all Predication, is Predication of Genus or Species, since the Attributives classed under the titles of Differentia, Proprium, Accidens, cannot be used but as part of the name of a Species. But we have seen, above, that Predication by Genus and Species is merely the substitution of one name for another, the more general for the less general; the fact of the substitution being marked by the Copula. It follows, if all Predication is by Genus and Species, that all Predication is the substitution of one name for another, the more for the less general.
It will be easy for the learner to make this material fact familiar to himself, by attending to a few instances. Thus, when it is said that man is rational, the term rational is evidently elliptical, and the word animal is understood. The word rational, according to grammatical language, is an adjective, and is significant only in conjunction with a substantive. According to logical language, it is a connotative term, and is without a meaning when disjoined from the object, the property or properties of which it connotes.[51]
[51] I am unable to feel the force of this remark. Every predication ascribes an attribute to a subject. Differentiae, Propria, and Accidents, agree with generic and specific names in expressing attributes, and the attributes they express are the whole of their meaning. I therefore cannot see why there should not be Predication of any of these, as well as of Genus and Species. These three Predicables, the author says, cannot be used but as part of the name of a genus or species: they are adjectives, and cannot be employed without a substantive understood. Allowing this to be logically, as it is grammatically, true, still the comprehensive and almost insignificant substantive, “thing” or “being,” fully answers the purpose; and the entire meaning of the predication is contained in the adjective. These adjectives, as the author remarks, are connotative terms; but so, on his own shewing elsewhere, are all concrete substantives, except proper names. Why, when it is said that man is rational, must “the word animal” be “understood?” Nothing is understood but that the being, Man, has the attribute of reason. If we say, God is rational, is animal understood? It was only the Greeks who classed their gods as ζῶα ἀθάνατα.
The exclusion of the three latter Predicables from predication probably recommended itself to the author as a support to his doctrine that all Predication is the substitution of one name for another, which he considered himself to have already demonstrated so far as regards Genus and Species. But proofs have just been given that in the predication of Genus and Species no more than in that of Differentia, Proprium, or Accidens, is anything which turns upon names the main consideration. Except in the case of definitions, and other merely verbal propositions, every proposition is intended to communicate a matter of fact: This subject has that attribute—This cluster of sensations is always accompanied by that sensation.
Let me remark by the way, that the word connote is here used by the author in what I consider its legitimate sense—that in which a name is said to connote a property or properties belonging to the object it is predicated of. He afterwards casts off this use of the term, and introduces one the exact reverse: but of this [hereafter].—Ed.
170 With respect, however, to such examples as this last, namely, all those in which the predicate consists 171 of the genus and differentia, the proposition is a mere definition; and the predicate, and the subject, are precisely equivalent. Thus, “rational animal” is precisely the same class as “man;” and they are only two names for the same thing; the one a simple, or single-worded name; the other a complex, or double-worded, name. Such propositions therefore are, properly speaking, not Predications at all. When they are used for any other purpose than to make known, or to fix, the meaning of a term, they are useless, and are denominated identical propositions.[52]