XIV. On the Fundamental Antithesis of Philosophy. By W. Whewell, D.D., 

 Master of Trinily College, and Professor of Moral Philosophy. 



[Read Feb. 5, 1844.] 



I HAVE upon former occasions laid before the Society dissertations on certain questions which 

 may be termed metaphysical : — on the nature of the truth of the laws of motion ; — on the ques- 

 tion whether all matter is heavy : — and on the question whether cause and effect are successive or 

 simultaneous. As these dissertations have not failed to excite some interest, I hope that I shall 

 have the indulgence of the Society in making a few remarl;s on another question of the same 

 kind. In doing this, as my object is to throw some light if possible on a matter of consider- 

 able obscurity and difficulty, I shall not attempt to avoid the occasional repetition of a sentence or 

 two which I may have, in substance, delivered elsewhere. 



1. All persons who have attended in any degree to the views generally current of the nature 

 of reasoning are familiar witii the distinction of necessary truths and truths of experience ; and few 

 such persons, or at least few students of mathematics, require to have this distinction explained 

 or enforced. All geometricians are satisfied that the geometrical truths with which they are con- 

 versant are necessarily true : they not only are true, but they must be true. The meaning of the 

 terms being understood, and the proof being gone through, the truth of the proposition must be 

 assented to. That parallelograms upon the same base and between the same parallels are equal ; — 

 that angles in the same segment are equal ; — these are propositions which we learn to be true 

 by demonstrations deduced from definitions and axioms; and which, when we have thus learnt them, 

 we see could not be otherwise. On the other hand, there are other truths which we learn from 

 experience ; as for instance, that the stars revolve round the pole in one day ; and that the moon 

 goes through her phases from full to full again in thirty days. These truths we see to be true ; 

 but we know them only by experience. Men never could have discovered them without looking 

 at the stars and the moon ; and having so learnt them, still no one will pretend to say that they 

 are necessarily true. For aught we can see, things might have been otherwise ; and if we had been 

 placed in another part of the solar system, then, according to the opinions of astronomers, experience 

 would have presented them otherwise. 



2. I take the astronomical truths of experience to contrast with the geometrical necessary trutlis, 

 as being both of a familiar definite sort; we may easily find other examples of both kinds of truth. 

 The truths which regard numbers are necessary truths. It is a necessary truth, that 27 and 38 

 are equal to (i5 ; that half the sum of two numbers added to half their difference is equal to 

 the greater number. On the other hand, that sugar will dissolve in water ; that plants cannot live 

 without light ; and in short, the whole body of our knowledge in chemistry, physiology, and the otlier 

 inductive sciences, consists of truths of experience. If there be any science which offer to us truths 

 of an ambiguous kind, with regard to which we may for a moment doubt whether they are neces- 

 sary or experiential, we will defer the consideration of them till we have marked the distinction of 

 the two kinds more clearly. 



3. One mode in which we may express the difference of necessary truths and truths of expe- 

 rience, is, that necessary truths are those of which we cannot distinctly conceive the contrary. 

 We can very readily conceive the contrary of experiential truths. We can conceive the stars moving 

 about the pole or across the sky in any kind of curves with any velocities ; we can conceive the 

 moon always appearing during the whole month as a luminous disk, as she might do if her 



