78 THE GRAMMAR OF SCIENCE 



seen, is termed a scientifit. law. The object served by the 

 discovery of such laws is the economy of thought ; the 

 suitable association of conceptions drawn from stored 

 sense-impressions, permits the fitting exertion to follow 

 with the minimum of thought upon the receipt of an 

 immediate sense-impression. The knowledge of scientific 

 law enables us to replace or supplement mechanical 

 association, or instinct, by mental association, or thought. 

 It is t\\e forethought, by aid of which man in a far higher 

 degree than other animals is able to make the fitting exer- 

 tion on the receipt of a novel group of sense-impressions. 

 We are accustomed to speak of scientific law, or at 

 any rate of one form of it termed " natural law," as some- 

 thing universally valid ; we hold it to be as true for all 

 men as for its original propounder. Nay, there are not 

 wanting those who assert that natural law has a validity 

 quite independent of the human minds which formulate, 

 demonstrate, or accept it. We can easily observe that 

 there is really something sni generis about the validity of 

 natural law. The philosopher who propounds a new 

 system, or the prophet who proclaims a new religion, may 

 be absolutely convinced of the truth of his statement ; 

 but it is the result of experience from time immemorial 

 that he cannot demonstrate that truth so that conviction 

 is produced in the mind of every rational being. A 

 philosophic or a religious formula — for example, the 

 idealism of Berkeley, the scepticism of Hume, or the self- 

 renunciation of the mediaeval mystics — however sure its 

 teachers may be that it is capable of rational demonstra- 

 tion, really appeals to the individual temperament, and is 

 accepted or rejected according to the emotional sympathies 

 of the individual. On the other hand, a formula, like 

 that which Newton propounded for the motion of the 

 planetary system, will be accepted by every rational mind 

 which has once understood its terms and clearly analysed 

 the facts which it resumes.^ This is sufficient to indicate 



1 One system of planetary gravitation is accepted throughout the civilised 

 world, but more than a dozen distinct theological systems and almost as many 

 philosophical schools hardly suffice even for our ojvn country. 



