INDUCTION AND DEDUCTION. 



A DISCOURSE BY JUSTUS BARON VON LIEBIG. 



DELIVERED I>f THE ROYAL ACADEMY OF 8CIEXCES, MUNICH. 



{Translated for the Smithsonian Institution.) 



The ideas of tbe generality of men respecting the natnre of scientific 

 research are so imperfect and erroneous that it will not, perhaps, be 

 without interest to many if I attempt to elucidate aud complete the 

 views which I advanced on this subject in a former discourse on Francis 

 Bacon, of Verulam. 



Philosophers pursue in general two methods of inquiry in regard to 

 the phenomena or laws of nature, induction and deduction ; they are in 

 eifect but different processes, while tlieir object is the same ; the dis- 

 tinction between them depends upon the point of outset ; the deductive 

 metliod sets out from generals, the inductive from particulars ; in the 

 combination of the two induction precedes deduction. 



The nature of induction, according to Aristotle's view of it, may per- 

 haps be best illustrated by the example which he himself gives of an 

 inductive conclusion : 



Mau, the horse, the mule, &c., live long. 

 Man, the horse, the mule, &c., have little gall. 

 Therefore, all auiruals that have little gall live loug. 



This mode of conclusion, if so we must call it, is a verj' easy oue to 

 the inquirer ; but what is here styled a conclusion is only the observa- 

 tion of the juxtaposition of two phenomena; scarcity of gall is a fact 

 which accompanies long life ; it is part of a whole, and the conclusion 

 no syllogism,, including in itself the reason of the dependence of longev- 

 ity on the i)aucity of the secretion in question. We need only substi- 

 tute in the middle term, instead of gall, any other simultaneous fact 

 peculiar to certain animals, for instance : 

 Horses, mules, &c., live long. 



fhave little gall. 

 Horses, mules, <! ^'^'''^ Slvcose in their muscular tissues. 

 I have uo uric acid, {Harnsaura.) 

 [ have (Hippursiiura) 



in order at once to perceive that the connection of these with longevity 

 is purely arbitrary and rests on no operation of the understanding. 

 The philosopher, for the explanation of a phenomenon of nature or of a 

 process, seeks to assign a connection between the parts thereof which 

 have come under his observation, and first of all sets out with the sup- 

 position, as regards two facts which constantly accompany the i)henome- 



