Deductive Logic

by George William Joseph Stock, M.A.

Part 2: Chapter 1

Additional Information
  • Year Published: 1888
  • Language: English
  • Country of Origin: England
  • Source: Stock, G. W. J. (1888). Deductive Logic. Oxford, England; Pembroke College.
  • Readability:
    • Flesch–Kincaid Level: 11.0
  • Word Count: 406
  • Genre: Informational
  • Keywords: math, math history
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Of the Proposition as distinguished from Other Sentences.

172. As in considering the term, we found occasion to distinguish it from words generally, so now, in considering the proposition, it will be well to begin by distinguishing it from other sentences.

173. Every proposition is a sentence, but every sentence is not a proposition.

174. The field of logic is far from being conterminous with that of language. Language is the mirror of man’s whole nature, whereas logic deals with language only so far as it gives clothing to the products of thought in the narrow sense which we have assigned to that term. Language has materials of every sort lying strewn about, among which the logician has to seek for his proper implements.

175. Sentences may be employed for a variety of purposes—

(1) To ask a question;

(2) To give an order;

(3) To express a feeling;

(4) To make a statement.

These various uses give rise respectively to

(1) The Interrogative Sentence;

(2) The Imperative Sentence;

(3) The Exclamatory Sentence;

(4) The Enunciative Sentence; Indicative Potential.

It is with the last of these only that logic is concerned.

176. The proposition, therefore, corresponds to the Indicative and Potential, or Conditional, sentences of grammar. For it must be borne in mind that logic recognises no difference between a statement of fact and a supposition. ‘It may rain to-morrow’ is as much a proposition as ‘It is raining now.’

177. Leaving the grammatical aspect of the proposition, we must now consider it from the purely logical point of view.

178. A proposition is a judgement expressed in words; and a judgement is a direct comparison between two concepts.

179. The same thing may be expressed more briefly by saying that a proposition is a direct comparison between two terms.

180. We say ‘direct comparison,’ because the syllogism also may be described as a comparison between two terms: but in the syllogism the two terms are compared indirectly, or by means of a third term.

181. A proposition may be analysed into two terms and a Copula, which is nothing more than the sign of agreement or disagreement between them.

182. The two terms are called the Subject and the Predicate ( 58).

183. The Subject is that of which something is stated.

184. The Predicate is that which is stated of the subject.

185. Hence the subject is thought of for its own sake, and the predicate for the sake of the subject.