14 THE PRINCIPLES OF SCIENCE. 



passing from more general to less general truths ; induc- 

 tion is the contrary process from less to more general 

 truths. We may however describe the difference in 

 another manner. In deduction we are engaged in develop- 

 ing the consequences of a law or identity. We learn 

 the meaning, contents, results or inferences, which attach 

 to any given proposition. Induction is the exactly inverse 

 process. Given certain results or consequences, we are re- 

 quired to discover the general law from which they flow. 



In a certain sense all knowledge is inductive. We can 

 only learn the laws and relations of things in nature by 

 observing those things. But the knowledge gained from 

 the senses is knowledge only of particular facts, and we 

 require some process of reasoning by which we may con- 

 struct out of the facts the laws obeyed by them. Expe- 

 rience gives us the materials of knowledge : induction 

 digests those materials, and yields us general knowledge. 

 Only when we possess such knowledge, in the form of 

 general propositions and natural laws, can we usefully 

 apply the reverse process of deduction to ascertain the 

 exact information required at any moment. In its ultimate 

 origin or foundation, then, all knowledge is inductive in 

 the sense that it is derived by a certain inductive 

 reasoning from the facts of experience. 



But it is nevertheless true, and this is a point to 

 which insufficient attention has been paid, that all reason- 

 ing is founded on the principles of deduction. I call in 

 question the existence of any method of reasoning which 

 can be carried on without a knowledge of deductive pro- 

 cesses. I shall endeavour to show that induction is really 

 the inverse process of deduction. There is no mode of 

 ascertaining the laws which are obeyed in certain pheno- 

 mena, except we previously have the power of determining 

 what results would follow from a given law. Just as the 

 process of division necessitates a prior knowledge of multi- 



