30 RULES FOR SAFE DEDUCTION. 



What an instructive caution against the hasty reception 

 of current phrases ! 



III. Bear constantly in view that the study of nature 

 is, mainly, the study of facts, not of causes ; and hence 

 that the objects of philosophical science are, not to 

 indulge in speculations and frame hypotheses,* but to 

 observe facts, to trace the phenomena of nature, to fix 

 their relations, and when possible, their order of suc- 

 cession, and to ascertain the facts that are universal. 

 The efficient causes being almost always beyond the 

 reach of the human faculties, are therefore not the 

 legitimate objects of scientific inquiry. 



In the deduction of general principles, the following 

 have been laid down as safe and unobjectionable rules : 



1. That whatever is assumed as a principle be itself 

 a fact, not an imaginary result of speculation. 



2. That it be true, without a single exception, of all 

 the individual cases ; or, in other words, that the fact be 

 universal. 



The first of these rules is specifically opposed to the 

 too prevalent habit of referring phenomena to fictitious 

 principles. The second is equally opposed to the 

 erroneous practice of hasty generalizing, or of inferring 

 some universal proposition from a limited number of 

 facts. 



IV. In your efforts to store your minds, while you 

 gather information from every source, exercise the 

 utmost caution as to the soundness of the principles you 

 adopt, or the authenticity of the facts which you admit ; 



* "Hypotheses non fingo," NEWTON remarks; "quicquid enim ex 

 phaenomenis non deducitur, hypothesis vocanda est. Et hypotheses, seu 

 metaphysicae seu physicae, seu qualitatum occultarum, seu mechanicas, 

 in philosophia experimentali locum non habent." Princip. lib. iii. 



