September i, 1914] 



SCIENCE 



349 



and to sociology. The entire critique, in 

 whicli the doctrine of Comte is carefully ap- 

 praised, hinges on the proposition that, 

 ", Strictly speaking, a theory can not he called 

 positive, unless it consists purely of verifiable 

 hypotheses." Those who hope that psycholog- 

 ical problems will ultimately receive physio- 

 logical solutions are not encouraged. The 

 same may be said of those who seek an ex- 

 clusively economic explanation of the facts of 

 history. 



The second chapter (of nearly 50 pages), 

 which deals with " facts and theories," opens 

 with a discussion of dreams and reality. What 

 is reality? What is its criterion? To make 

 a genuine contribution to the literature of 

 that hoary question is something of an 

 achievement. Enriques has made such a con- 

 tribution. The conclusion is that " the true 

 characteristic of reality is the correspondence 

 of the sensations with the expectation." Real- 

 ity is thus defined as an invariant, a mathe- 

 matical term that is gaining currency in vari- 

 ous branches of natural science. " There are 

 certain fixed groupings, independent of us, 

 among our actual or supposed volitions on the 

 one hand, and the sensations produced by 

 them on the other. These groupings corre- 

 spond to what we call the real." The real thus 

 is " an invariant in the correspondence be- 

 tween volition and sensation." The definition 

 involves a hypothetical element : it is presup- 

 posed that actual sensations would recur if 

 their conditions were reproduced; but such re- 

 production is frequently impossible. This 

 conception of reality is examined in relation 

 to the past, to psychology, to society, to biol- 

 ogy, to physics, to astronomy and so on. 

 What of hallucinations? The problem is 

 frankly recognized but no pretense of a solu- 

 tion is made. A valuable suggestion, however, 

 is offered. It is that " the patients are unable 

 to doubt and so submit their false impressions 

 to a critical proof directed by the will." The 

 object of an hallucination is unreal because 

 the subject's deception is real. How does 

 knowledge pass from common facts to scien- 

 tific facts ? The answer is : by passing from 

 the subjective or individual view to the objec- 



tive or social view, from the personal to the 

 impersonal view. A common fact is a fact 

 viewed in relation to the beholder ; a scientific 

 fact is a fact viewed in relation to surround- 

 ing facts. " If I strike a copper plate with a 

 hammer, the plate grows hot," is a common 

 fact. " Bodies are heated by percussion " is a 

 scientific fact. Thus the conception of scien- 

 tific fact merges into that of law. What is 

 the relation of hypothesis to scientific knowl- 

 edge or knowledge of reality ? " To make an 

 hypothesis signifies : (1) to expect or to fore- 

 see given sensations under certain future con- 

 ditions; (2) to arrange among the groups of 

 actual or controllable sensations, an inter- 

 mediate grouping which shall serve to associ- 

 ate them in a given order of prevision." This 

 view of the function of hypothesis is elabo- 

 rated very instructively in connection with 

 such topics as the value of scientific knowl- 

 edge; knowledge by means of concepts, em-' 

 piricism and rationalism, the acquisition of 

 knowledge, scientific theories, the theory of 

 gravitation, the electrostatic theory of Pois- 

 son, the theory of solutions and the economy 

 and the psychological development of theories. 

 This many-sided critique of the scientific 

 role of hypothesis leads naturally to the ques- 

 tion of the ofBces of induction and deduction 

 in epistemology, and the third chapter (72 

 pages) is accordingly devoted to problems of 

 logic. To the oft-repeated stupid charge that 

 formal reasoning can not lead to gain of 

 knowledge, our author justly replies that such 

 reasoning serves as an instrument of trans- 

 formation which, though it does not alter the 

 conceptual data of knowledge, but leaves their 

 truth or falsity to be shown by other means, 

 yet establishes a connection whereby the truth 

 or falsity of certain data implies the truth or 

 falsity of other data. For example, formal 

 logic may show that an hypothesis M implies 

 a consequence G, and it often happens that we 

 can test G directly and thus test H indirectly. 

 The work of induction and deduction is team 

 work. Science can not dispense with either of 

 them. The importance of modern develop- 

 ments in symbolic logic is recognized. An 

 exceedingly valuable discussion of the nature, 



