20 PART I. THE PROBLEM. 



circumstances, without a union of several perhaps of all, the 

 sciences" (Sir John Herschel, Discourse, [183.]), a sentiment 

 which the eminent physicist Lord Kelvin endorses by saying : 

 "All the properties of matter are so closely connected that we 

 can scarcely imagine one thoroughly explained, without our 

 seeing its relation to all the others, without, in fact, having the 

 explanation of all." (The Constitution of Matter, 1901, p. 240.) 

 The common experience of one science dividing into a number 

 of others is a further verification of the above contention: "By 

 a law whose necessity is evident, each branch of the scientific- 

 system gradually separates from the trunk when it has de- 

 veloped far enough to admit of separate cultivation." (Auguste 

 Comte, The Fundamental Principles of the Positive Philosophy, 

 ed. 1905, p. 31.) 



Some logicians have also thought that only instinct, sagacity, 

 imagination, and other alleged unanalysable mental qualities 

 can be advantageously utilised in the process of scientific 

 enquiry. As opposed to this view, i. e., that scientific ability is 

 an indeterminate X, and science itself necessarily absolute, we 

 shall endeavour to show in the sequel that an art of reasoning 

 relating to greater or smaller probabilities of an imperfectly 

 calculable character has developed through the ages, and may 

 be abstracted from the present practice of men of science. 

 Some writers on logic (Bosanquet, in his Logic, and Creighton, 

 in his Introductory Logic) argue that the reasoning process 

 presents a developing unity ; and it is to be hoped that logicians 

 generally will recognise that progressive stages of proof and of 

 certainty deserve to be circumstantially treated in works on logic. 



Psychologists have spoken of the psychologist's fallacy. One 

 might with equal justice speak of the logician's fallacy. The 

 final product of a process of reasoning stated in formal terms 

 has been mistaken for the expression of the concrete process 

 itself, and reasoning in formal terms and modes has been 

 assumed as the only mode of reasoning. Logic is, however, 

 a progressive science, as we shall see. (Section VI.) In pro- 

 portion as convention favours the utilisation or the neglect 

 of hypotheses, so men accustom themselves to the one or the 

 other; as generalising is or is not encouraged, or as abstract 

 or concrete, dignified or petty interests prevail, so men adjust 

 their thoughts in conformity with the social trend; and when 

 reliance on books or on imaginative treatment rules, when it 

 is the fashion to think with or without aids, formally or in- 

 formally, the scientific mass mind faithfully reflects each of 

 these trends. This being the case, it may be conjectured, with 

 some degree of certainty, that the average individual of the 

 somewhat distant future as the eventual result of the discovery 

 and the assimilation by the masses of mankind of the modes 

 of thought which time has ripened, and which the modern 

 scientist at his best applies when engaged in expert investi- 



