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Every enunciative speech must have à verb, or some variation of a verb. Affirmation is the enunciation of one thing concerning another. Negation is the enunciation of one thing from another. Contradiction is an affirmation and negation that are opposite. This is a summary of the first six chapters.
The seventh and eighth treat of the various kinds of enunciations or propositions, universal, particular, indefinite, and singular; and of the various kinds of opposition in propositions, and the axioms concerning them. These things are repeated in every system of logic. In the ninth chapter, he endeavours to prove, by a long metaphysical reasoning, that propositions respecting future contingencies are not, determinately, either true or false; and that if they were, it would follow, that all things happen necessarily, and could not have been otherwise than as they are. remaining chapters contain many minute observations concerning the equipollency of propositions both pure and modal.
SECT. 1. On the Five Predicables.
HE writers on logic have borrowed their materials almost entirely from Aristotle's Organon and Porphyry's Introduction. The Organon, however was not written by Aristotle as one work. It comprehends various tracts, written without the view of making them parts of one whole, and afterwards thrown together by his editors under one name on account of their affinity. Many of his books that are lost, would have made a part of the Organon if they had been saved.
The three treatises of which we have given a brief account, are unconnected with each other, and with those that follow. And although the first was undoubtedly compiled by Porphyry, and the two last probably by Aristotle, yet I consider them as the venerable remains of a philosophy more ancient than Aristotle. Archytas of Tarentum, an eminent mathematician and philosopher
of the Pythagorean school, is said to have wrote upon the ten categories; and the five predicables probably had their origin in the same school. Aristotle, though abundantly careful to do justice to himself, does not claim the invention of either. And Porphyry, without ascribing the latter to Aristotle, professes only to deliver the doctrine of the ancients and chiefly of the Peripatetics, concerning them.
The writers on logic have divided that science into three parts; the first treating of simple apprehension and of terms; the second, of judgment and of propositions; and the third, of reasoning and of syllogisms. The materials of the first part are taken from Porphyry's introduction and the Categories; and those of the second from the book of Interpretation.
A predicable, according to the grammatical form of the word, might seem to signify, whatever may be predicated, that is, affirmed or denied, of a subject and in that sense, every predicate would be a predicable. But logicians give a different meaning to the word. They divide propositions into certain classes, according to the relation which the predicate of the proposition bears to the subject. The first class is that wherein the predicate is the genus of the subject; as when we say, This is a triangle, Jupiter is a planet. In the second class, the predicate is a species of the subject; as when we say, This triangle is right-angled. A
third class is when the predicate is the specific difference of the subject; as when we say, Every triangle has three sides and three angles. A fourth when the predicate is a property of the subject; as when we say, The angles of every triangle are equal to two right angles. And a fifth class is when the predicate is something accidental to the subject; as when we say, This triangle is neatly drawn.
Each of these classes comprehends a great variety of propositions, having different subjects, and different predicates; but in each class the relation between the predicate and the subject is the same. Now it is to this relation that logicians have given the name of a predicable. Hence it is, that although the number of predicates be infinite, yet the number of predicables can be no greater than that of the different relations which may be in propositions between the predicate and the subject. And if all propositions belong to one or other of the five classes above mentioned, there can be but five predicables, to wit, genus, species, differentia, proprium, and accidens. These might, with more propriety perhaps, have been called the five classes of predicates; but use has determined. them to be called the five predicables.
It may also be observed, that as some objects of thought are individuals, such as, Julius Cæsar, the City Rome: so others are common to many individuals, as good, great, virtuous, vicious. Of this last kind are all the things that are expressed by adjectives.
jectives. Things common to many individuals, were by the ancients called universals. All predicates are universals, for they have the nature of adjectives; and, on the other hand, all universals may be predicates. On this account, universals may be divided into the same classes as predicates; and as the five classes of predicates above mentioned have been called the five predicables, so by the same kind of phraseology they have been called the five universals; although they may more properly be called the five classes of universals.
The doctrine of the five universals or predicables makes an essential part of every system of logic, and has been handed down without any change to this day. The very name of predicables shews, that the author of this division, whoever he was, intended it as a complete enumeration of all the kinds of things that can be affirmed of any subject; and so it has always been understood. It is accordingly implied in this division, that all that can be affirmed of any thing whatever, is either the genus of the thing, or its species, or its specific difference, or some property or accident belonging to it.
Burgersdick, a very acute writer in logic, seems to have been aware, that strong objections might be made to the five predicables, considered as a complete enumeration; but, unwilling to allow any imperfection in this ancient division, he endeavours to restrain the meaning of the word predicable,