ii SCIENTIFIC RECONSTRUCTION 257 



in a given space is equal to the acceleration of that body 

 or of any other body which is not susceptible of a different 

 rate of acceleration. If, finally, from this definition, the 

 term body be omitted as not capable of resolution into 

 terms of motion pure and simple, the equation becomes a 

 pure tautology. As such it acquires the appearance of 

 an axiom, but the moment that the question of its truth 

 gives place to that of its application, the fining down of its 

 terms which engenders the axiomatic appearance is for- 

 gotten. P becomes an expression for c forces ' taken as 

 real, pressures, strains, stresses, impacts, attractions, and 

 mass becomes an ultimate property of the very matter which 

 the physicist, in his more critical moments, is almost 

 inclined to declare unknowable, while the whole equation, 

 as a result, is a law of the material universe from which the 

 most far-reaching deductions as to the origin and destiny 

 of things can be drawn. In short, in science as in meta- 

 physics there is tendency of ultimate principles to play a 

 double part. To obtain certainty of proof their terms 

 are fined down to a point approximating to tautology, to 

 a point in which, at best, they express the mutual relations 

 of certain concepts. To obtain meaning and width of 

 application the same terms are again expounded to cover 

 the real working of forces that may be but imperfectly seen 

 and known, and are by no means to be controlled by human 

 definitions. 



4. What may be called the Hypothetical stage in the 

 development of science moves between two poles of 

 fallacy. In its assumptions about the real nature of things, 

 it goes beyond its warrant, and commits itself to that which 

 its inverse method cannot prove. If to escape this it fines 

 down its concepts to elements which can be educed from 

 experience by analysis, it relapses into a mere construction 

 of a conceptual order with but a casual and uncertain appli- 

 cation to reality. So far as it oscillates between the two 

 points of view, it falls into sheer fallacy, and so far as it 

 confines itself to the description of what is given, it 

 abandons the attempt to construe the real order. 



At its best the inverse method is an advance on the self- 



