148 THE SCIENCE OF LOGIC 



233. SUMMARY OF LOGICAL REQUIREMENTS FOR A LEGITI 

 MATE HYPOTHESIS. We may now briefly recapitulate the condi 

 tions required for a legitimate scientific hypothesis. 



I . // must be based on preliminary observation of some fact or 

 groups of facts, be invented in order to explain them, and therefore 

 have for its object a real cause, a &quot; vera causa &quot;, This rule excludes 

 all subjective suppositions employed as aids to the imagination 

 (226). It also excludes all purely fanciful guesswork about causes. 

 Observed uniformities in facts must suggest hypotheses ; these must 

 not be constructed entirely from imagination ; they must have a 

 basis in accurate and unbiased observation of the facts ; they 

 must not be merely preconceived notions which we allow ourselves 

 to read into the facts. &quot; The scientist,&quot; writes Claude Bernard, 

 &quot;should have an hypothesis to verify; but he ought to make 

 sure that the facts on which it is based be accurately and imparti 

 ally observed. Hence he should be an observer no less than an 

 experimenter. As observer, he will simply and solely register 

 the phenomenon under observation. He will be, so to speak, a 

 photographer of phenomena : his observation will be a faithful re 

 presentation of nature, free from all prejudiced and preconceived 

 ideas. As observer, he will be passive, silent, receptive ; he will 

 listen to nature, and write under her dictation. Then, once he 

 has carefully observed the phenomenon, he will conceive an hypo 

 thesis and proceed to test it experimentally.&quot; * We must, there 

 fore, observe the facts without preconceived ideas ; that is, we 

 must observe before supposing, not vice versa. Simple as this 

 recommendation is in its formulation, it is by no means easy to 

 carry out in practice. Our initial observation and determination 

 of the phenomenon to be investigated must be impartial, not 

 biased by any preconceived views. Then, when we have conceived 

 our hypothesis, and proceed to test it by renewed observation and 

 experiment, we must resist all inclination to interpret the facts in 

 favour of it. We must be ever ready to modify or reject it. 

 Just as the wish can be father to the thought, so can attachment 

 to an hypothesis easily misguide and distort our reading of the 

 facts. It is difficult to guard against this undue influence while 

 we are conducting our observations and experiments for the 

 express purpose of testing our hypotheses. It is to secure impar 

 tiality in this testing process that Claude Bernard says to the 



1 CLAUDE BERNARD, Introduction d Vitude de la midecine expirimentale, pp. 

 39-4- 



