The principles of science : a treatise on logic and scientific method / by W. Stanley Jevons.

  • William Stanley Jevons
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The principles of science : a treatise on logic and scientific method / by W. Stanley Jevons. Source: Wellcome Collection.

    86/488 (page 66)
    the propositions are of the form A = AB B = c; whence, by substitution, A = Ac. Inference of a Partial from Two Partial Identities. However common be the cases of inference already noticed, there is a form occurring almost more frequently, and which deserves much attention because it occupied a prominent place in the ancient syllogistic system. That system strangely overlooked all the kinds of argument we have as yet considered, and selected as the type of all reasoning one which employs two partial identities as premises. Thus from the propositions Sodium is a metal (i) Metals conduct electricity, (2,) we may conclude that Sodium conducts electricity. (3) Taking A, B, C, respectively to represent the three terms, the premises are of the form A = AB (i) B = BC. (2) Now for B in (i) we can substitute its description as given in (2), obtaining A = ABC, (3) or, in words, from Sodium = sodium metal (i) Metal = metal conducting electricity, (2) we infer Sodium = sodium metal conducting electricity, (3) which in the elliptical language of common life becomes ' Sodium conducts electricitv.'