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

  • Jevons, William Stanley, 1835-1882.
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.

    77/488 (page 57)
    Venus, and Venus must differ from Mars. The Earth diifers from Jupiter in density; therefore Jupiter must differ from the .Earth. Speaking generally, if A ~ B we shall also have B -»- A, and these two forms may be con sidered expressions of the same difference. But the reader will notice that the relation of differing things is not wholly reciprocal. The density of Jupiter does not differ from that of the Earth in the same way that that of the Earth differs from that of Jupiter. The change of sensation which we experience in passing from Venus to Mars is not the same as what we experience in passing back to Venus, but just the opposite in nature. The colour of the sky is lighter than that of the ocean; therefore that of the ocean cannot be lighter than that of the sky, but darker. In these and all similar cases we gain a notion of direction or character of change, and results of immense importance may be shown to rest on this notion. For the present we shall be concerned with the mere fact of identity existing or not existing. Twofold Interpretation of Propositions. Terms, as we have seen (p. 31), may have a meaning either in extension or intension; and according as one or the other meaning is attributed to the terms of a proposition, so may a different interpretation be assigned to the proposition itself: When the terms are abstract we must read them in intension, and a proposition con necting such terms must denote the identity or non- identity of the qualities respectively denoted by the terms. Thus if we say Equality = Identity of magnitude, the assertion means that the circumstance of being equal