134 GENERAL Y1EW AND BASIS OF SCIENTIFIC RESEARCH. 



ground,' and who ' asserts that, if placed in scales, she can 

 make herself lighter by an act of will ! ' 



One of the most frequent sources of error is too exten- 

 sive generalisation, and relying too much upon insufficient 

 evidence. Men of science may, and do with safety, tem- 

 porarily entertain all kinds of scientific questions and ideas 

 which are possible to be conceived, whether they have 

 been proved by evidence or not ; but usually only as un- 

 certain hypotheses. No careful investigator employs an 

 hypothesis which he knows is a doubtful one, nor adopts 

 an unproved hypothesis as a fixed belief, but uses it only 

 for the temporary purpose of testing whether it is true 

 or false. Every such investigator also soon rejects ques- 

 tions which manifestly contradict the fundamental laws 

 of the sciences. As also the conceivable is not neces- 

 sarily true, nor the inconceivable necessarily false, we may 

 justifiably assume even the most apparently ridiculous 

 idea, provided we hold it only as a temporary and unfixed 

 hypothesis. 



Violation of logical rules and methods is a very com- 

 mon source of error. In all unsettled questions, the 

 chances of drawing wrong conclusions are numerous, and 

 of forming correct ones very few. In some cases the data 

 we infer from are false, and in others insufficient. Some- 

 times the conclusions we draw exceed the extent of the 

 premises ; i.e. we endeavour to prove too much. We are 

 extremely apt to reason from our own experience alone, 

 instead of from that of all mankind ; and even the latter 

 is often very incomplete. In some cases our statements 

 are logically true, but materially false, and in others 

 materially false but formally true. In other cases, by 

 neglecting to arrange and combine the evidence in all 

 the ways it logically admits of, we fail to extract from 

 our results and general conclusions as much knowledge as 



