226 ON THOUGHT IN MEDICINE. 



In order to acquire this foreknowledge of what is 

 coming, but of what has not been settled by obser- 

 vations, no other method is possible than that of 

 endeavouring to arrive at the laws of facts by observa- 

 tions; and we can only learn them by induction, by the 

 careful selection, collation, and observation of those cases 

 which fall under the law. When we fancy that we have 

 arrived at a law, the business of deduction commences. 

 It is then our duty to develop the consequences of our 

 law as completely as may be, but in the first place only 

 to apply to them the test of experience, so far as they 

 can be tested, and then to decide by this test whether 

 the law holds, and to what extent. This is a test 

 which really never ceases. The true natural philo- 

 sopher reflects at each new phenomenon, whether the 

 best established laws of the best known forces may 

 not experience a change ; it can of course only be a 

 question of a change which does not contradict the whole 

 store of our previously collected experiences. It never 

 thus attains unconditional truth, but such a high degree 

 of probability that it is practically equal to certainty. 

 The metaphysicians may amuse themselves at this ; we 

 will take their mocking to heart when they are in a 

 position to do better, or even as well. The old words 

 of Socrates, the prime master of inductive definitions, 

 in reference to them are just as fresh as they were 

 2,000 years ago : c They imagined they knew what they 



