42 THE METHOD OF SCIENCE 



systems is invented, not that he may admire it and follow it in all 

 its consistent consequences, but that he may make it the occasion 

 of a course of active experiment and observation. And if the 

 results of this process contradict his fundamental assumptions, 

 however ingenious, however symmetrical, however elegant his 

 system may be, he rejects it without hesitation. He allows no 

 natural yearnings for the offspring of his own mind to draw him 

 aside from the higher duty of loyalty to his sovereign, Truth : to 

 her he not only gives his affections and his wishes, but strenuous 

 labour and scrupulous minuteness of attention." * 



72. In science, therefore, we must not only use words that 

 express our meanings unmistakably, 2 we must not only verify our 

 facts, but we must always test our thinking deductively " by observ- 

 ing the present state of the world, by assiduously studying the 

 history of past ages, by sifting the evidence of facts, by carefully 

 combining and contrasting those which are authentic, by generaliz- 

 ing with judgment and diffidence, by perpetually bringing the 

 theory we have constructed to the test of new facts, by correcting 

 or altogether abandoning it, according as the new facts prove it to 

 be partially or fundamentally unsound." 3 All this is axiomatic, 

 and has been axiomatic since men began to think scientifically. 

 Therefore it would be difficult to conceive anything more absurd 

 than the statement that we must eschew deduction and rely wholly 

 on induction. " All inductive reasoning is but the inverse applica- 

 tion of deductive reasoning. Being in possession of certain 

 particular facts or events expressed in propositions, we imagine 

 some more general proposition expressing the existence of a law 

 or cause ; and deducing particular results of that supposed general 

 proposition, we observe whether they agree with the facts in 

 question." 4 Induction and deduction " differ only as the road by 

 which we ascend from a valley to a mountain does from that by 

 which we descend from the mountain to the valley, which is no 

 difference of road, but only a difference in the going." 5 Induction is 

 that process by which we infer a generalization from a consideration 

 of particular facts or from a consideration of inferior inductions, 

 each of which is then used as a fact. Thus it is an induction which 

 has been drawn a thousand times that parental ill-health results in 

 innately enfeebled offspring. It is also a common induction that 

 it has no such effect on offspring. Deduction is the process 



1 Whewell, Novum Organum Renovatum, pp. 80- 1. 



2 See chapter i. 3 Macaulay. 



4 Jevons, Principles of Science, p. 265. 6 Port Royal Logic, p. 314. 



