2ET.46.] TO JAMES D. DANA. 431 



bound to try all the steps of the reasoning, and all the 

 facts it rests on, impartially, and even to suggest all 

 the adverse criticism I can think of. When I read 

 the pamphlet I jotted down on the margin some notes 

 of what struck me at the time. I will glance at them 

 again, and see if, on reflection, they appear likely to 

 be of the least use to you, and if so will send them, 

 taking it for granted that you rather like to be criti- 

 cised, as I am sure I do, when the object is the surer 

 establishment of truth. 



In your idea of species as specific amount or kind 

 of concentrated force, you fall back upon the broadest 

 and most fundamental views, and develop it, it seems 

 to me, with great ability and cogency. 



Taking the cue of species, if I may so say, from the 

 inorganic, you develop the subject to great advantage 

 for your view, and all you say must have great weight, 

 in " reasoning from the general." 



But in reasoning from inorganic species to organic 

 species, and in making it tell where you want it and 

 for what you want it to tell, you must be sure that 

 you are using the word " species " in the same sense in 

 the two, that the one is really an equivalent of the 

 other. That is what I am not yet convinced of. And 

 so to me the argument comes only with the force of an 

 analogy, whereas I suppose you want it to come as 

 demonstration. Very likely you could convince me 

 that there is no fallacy in reasoning from the one to 

 the other to the extent you do. But all my experi- 

 ence makes me cautious and slow about building too 

 much upon analogies ; and until I see further and 

 clearer, I must continue to think that there is an 

 essential difference between kinds of animals or plants 

 and kinds of matter. How far we may safely reason 



