352 NECESSARY TRUTH 



resume or brief expression of the relations and sequences of certain 

 of these perceptions and conceptions, and exists only when 

 formulated by man. 1 . . . The law of gravitation is not so much 

 the discovery by Newton of a rule guiding the motion of the 

 planets as his invention of a method of briefly describing the 

 sequences of sense-impressions, which we term planetary motion. . . . 

 We are thus to understand by a ' law of nature,' a resumed mental 

 shorthand, which replaces for us a lengthy description of the 

 sequences among our sense impressions." 2 According to the law 

 of gravitation, all bodies in nature attract each other proportion- 

 ately as their masses andjnversely as the squares of their distances. 

 Now in what intelligible sense can the sense-impression, the earth, 

 be said to attract the sense-impression, the sun ? What are their 

 masses, and what the squares of their distances ? To all appear- 

 ances the planets, the sun, and the other stars are of no great 

 magnitudes, at no great distances, and float lighter than feathers 

 through the air. Even if they be conceived as nothing more than 

 sense-impressions between which, after a previous training by 

 common sense, Newton was able to discover relations which are 

 quite unlike their apparent relations, how do we know that Newton 

 existed as a thinking entity? As a fact, the law of gravitation 

 has been accepted by astronomers and physicists as describing a 

 relationship between material bodies external to the human mind 

 bodies and a relationship between them which the human mind is 

 thought to be aware of at present, but which existed long before 

 the evolution of any such mind. Obviously also, since the word 

 1 attraction ' is used, the relationship indicated, as in the case of 

 many other laws that have been formulated, is one of causation. 

 It is not a mere invariable succession such as that of night and 

 day, the notion of which is reached, not through a consideration 

 of the qualities of the related objects, but through simple enumera- 

 tion. I say ' formulated,' for the laws that are reached through 

 simple enumeration (e.g. the law that all material bodies have 

 extension), are, as a rule, discovered by every one and therefore 

 are not worth formulating by anyone. 



591. " In the scientific sense, a law is a statement of a necessary 

 connexion ; it is not something imposed upon reality from without, 

 but is the outcome of the nature of reality itself. The perception 

 of natural laws is due, no doubt, to the synthetic activity of mind, 

 but it is possible only because the connexion actually exists in 

 reality. It is because the world is a systematic unity that we are 

 1 Pearson, Grammar of Science, ed. 1900, p. 82. z Op. ctt., p. 86-7. 



