48 THE METHOD OF SCIENCE 



inductions ; next we ascertain by deduction whether the separate 

 inductions are in harmony with each other and with reality in 

 general ; and, lastly, treating each induction as a fact, we bind 

 them together in a wider induction " To the Deductive Method, 

 thus characterized in its three constituent parts, Induction, Ratio- 

 cination, and Verification, the human mind is indebted for its 

 most conspicuous triumphs in the investigation of nature." l " At 

 any step of Induction . . . the inductive proposition is a Theory 

 with regard to the Facts it includes, while it is to be looked upon 

 as a Fact with respect to the higher generalizations in which it is 

 included. In any other sense . . . the opposition of Fact and 

 Theory is untenable, and leads to endless perplexity and debate. 

 Is it a Fact or a Theory that the planet Mars revolves in an ellipse 

 about the Sun ? To Kepler, employed in endeavouring to combine 

 the separate observations by the conception of an Ellipse, it is a 

 Theory ; to Newton, engaged in inferring the law of force from a 

 knowledge of the elliptical motion, it is a Fact. There are . . . 

 no special attributes of Theory and Fact which distinguish them 

 from one another. Facts are phenomena apprehended by the 

 aid of conceptions and mental acts as Theories also are. We 

 commonly call our observations Facts, when we apply, without 

 effort or consciousness, conceptions perfectly familiar to us, while 

 we speak of Theories when we have previously contemplated the 

 Facts and the connecting Conceptions separately, and have made 

 the conception by a conscious mental act." 2 



established inferences of mathematics and physics have been proved thus. It follows 

 that the aim of the student of heredity and evolution is to discover laws and so con- 

 vert biology into a deductive science. If he proceeds according to the method by 

 which alone interpretative science has been created hitherto, he will begin by col- 

 lecting and verifying relevant facts ; on these facts he will found inferences ; and 

 these hypotheses he will endeavour to test in every direction possible by the only 

 means possible by deductive appeals to reality. This last step will not only 

 establish his hypotheses if true, or disprove them if untrue, but it will also bring 

 within their range numbers of facts which would not otherwise have been thought 

 of in connection with them. The history of such biological work as has involved 

 thinking about the sequences of phenomena about cause and effect indicates 

 very clearly that almost every controversy has arisen because the ordinary rules 

 of logical and scientific method were neglected. Facts have been incorrectly 

 described, or they have not been verified, or hypotheses incapable of proof have 

 been formulated, or hypotheses capable of proof have not been tested, or opponents 

 have ignored the proofs. Owing largely to the care with which facts are verified 

 and hypotheses tested, and the readiness with which proofs are accepted, contro- 

 versies are relatively rare amongst the students of physics, and rarer still amongst 

 mathematicians. (See Mill, Logic, Bk. III., from which a passage is quoted as foot- 

 note to 352. See also chapters xviii. and xxv. of the present work.) 



1 See Mill, Logic, III. ii. 3. 2 Whewell, Novum Organum Renovatum, p. 116. 



