As the Term is the external expression of the Concept, so the Proposition is the expression of the Judgment. The Proposition may be defined as a verbal expression in which we affirm or deny an attribute of a subject (de Interp. c. 6, sect; 1).
It is also sometimes defined as a verbal expression enunciating a truth or falsity (de Interp. c. i): for it is characteristic of every proposition that it must be either true or false. The form of the proposition is S is (or is not) P, e.g. 'The lion is vertebrate', 'Caesar is not alive'.
A proposition of the kind we have described, is commonly known as the Categorical Proposition, to distinguish it from Conditional Propositions. In these we do not assert the attribute of the subject absolutely: we merely affirm that, given certain conditions, it belongs to it.
In regard to the Categorical proposition, the following points are to be noted —
(1) It is always in the indicative mood. In the other grammatical moods, the mind does not judge that the attribute belongs to the subject, but expresses a wish that it may be so, or gives an injunction that it should be so. In the indicative alone we affirm (or deny) the attribute of the subject. Thus we have, "The messenger is speaking", "May the messenger speak?" "Speak, messenger!" So too it is only when the attribute is affirmed of the subject that the mind reaches truth or falsity. For truth is attained when the mind assigns to the subject an attribute which belongs to it in the real order.
(2) The logical proposition is always stated in the present tense. Our purpose in Logic, as we have seen, is to study the mode in which the mind represents the real order. As regards this the question of present, past or future is purely accidental. The time-determination does not affect the mental representation as such. Hence differences of tense so necessary in the use of language for practical ends have no place in Logic. (3) The logical predicate is always separated from the copula. In the language of common life, we frequently express them in one word, as for instance, 'The bird flies'. In Logic we must say, 'The bird is flying.'
This same process must be performed whenever we get mutilated expressions, such as 'Wolf!' 'Fire!' 'Rain!' For Logic demands that every sentence, whatever its grammatical form, shall be so analysed and expressed, as to represent as closely as possible the intellectual act.
Sir W. Hamilton stated this in what is sometimes termed Hamilton's Postulate, viz. 'Logic postulates to be allowed to state explicitly in language, whatever is implicitly contained in thought.' Our three mutilated expressions may be respectively resolved into, 'A wolf is near,' 'A fire is burning,' 'Rain is falling.'
We must carefully distinguish between the 'is' of the copula, and the same word when it means ‘to exist’. This point will be treated at length later. Here it will be sufficient to note that the copula does not necessarily imply that the subject exists.¹
Its office in affirmative sentences is to denote the objective identity of the subject and predicate: that they are expressions representing one and the same object. In negative sentences the copula 'is not' signifies the objective diversity of the terms: the predicate is not applicable to the object denoted by the subject. I may say, 'The lion is vertebrate,' because the term 'vertebrate' is rightly applied to the same object as the term 'lion’. I cannot say ‘The octopus is vertebrate’. This relation between the subject and predicate of the proposition, arises immediately from the nature of the mental act which the pro position represents — the judgment. In every affirmative judgment the two terms are different mental expressions of the same object. The same object is expressed in one concept as 'lion’, in another as 'vertebrate’. But the object which I conceive as 'octopus’, I cannot conceive also as 'vertebrate’. Hence the judgment’, The octopus is vertebrate’, is impossible.
Here we see how totally Scholastic Logic differs from Formal Logic. Strictly, Formal Logic should take no account of the content of the subject and predicate. To it every judgment is simply S is P. Scholastic Logic rejects any judgments in which the concepts do not represent the same objective reality, e.g. 'Men are circles’, 'Cows are lions’. In these the two notions are repugnant the one to the other. The judgment is impossible.
Analysis of the Judgment.
Although as we have seen, the subject and predicate of the judgment are different concepts of the same thing, it is important to bear in mind that it is the subject which directly expresses the thing, i.e. that to which attributes belong. The predicate expresses the thing as qualified by a particular attribute or form.²
Whenever we fix our attention on a thing, our mind immediately commences to abstract the attributes from the object of thought, and affirm them of it one by one. It judges: 'The thing is hard — is black — is brittle, etc.' ³ Here the predicate in each case is the attribute or form —not indeed the attribute considered in separation from the object in which it inheres, i.e. hardness, blackness, etc., but considered as qualifying the thing.
It is easy to see how such judgments develop into more complex ones. The hard, brittle thing will be called 'coal': and the judgment will take predicates of a less primary character.1
A judgment is said to be true when the form expressed by the predicate is really found in the object denoted by the subject. Thus, if I see some object, e.g. Socrates, and I judge 'Socrates is walking,' my judgment is a true one if the attribute 'walking’, which I affirm of Socrates in thought, does in fact belong to him in the real order.
Hence truth is defined as the conformity of the mind with its object. For in every true affirmative judgment the mental concept expressed in the predicate is in conformity with a real attribute belonging to the external object.
As regards negative judgments the case is somewhat different. In them we declare that the form expressed in the predicate is not to be found in the object to which the judgment refers. Yet in a somewhat wide sense we can say that in negative judgments also the mind is conformed to its object. In judging a form not to belong to an object which in fact does not possess it, my mind is in correspondence with reality. But negation is a secondary and subsidiary form of truth. In affirmation there is perfect correspondence between the mental form expressed in the predicate and the objective reality. (I. Sent. d. 19, Q. 5, Art. i, ad. i.).
Grammatically the subject does not always take the first place. It is the meaning of the proposition, not the arrangement of the words, which tells us which is the subject and which the predicate. The term which qualifies or defines the other, whether it comes first or last, is the predicate. Thus in the words, 'Blessed are the meek,' it is the meek who form the logical subject.
What has just been said will throw light on the nature of the third element of the proposition — the copula.
The Copula: While the predicate expresses one of the forms which
determine the subject, thus telling us what the thing is, the copula
expresses the being which is thus determined.
¹The question of the 'Implication of Existence' in the copula, will be more fully dealt with in Ch 7.
Cf. St. Thomas, Summa Theol. I. Q. 53, Art. 12.
² "c'est donc grace a. 1'abstraction intellectuelle que
les choses sont affirmables les unes des autres, et peuvent faire fonction
de predicat dans les propositions." Mercier, sect; 31. And Themistius
says on Arist.: "The sense-faculty gives us the phantasm of Socrates
walking as a single whole: the intellect abstracts, and separates Socrates
on the one hand from is walking on the other." Them.
202, 10 cited in Rodier, Traite de I'ame. II. 471.
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