520 LETTERS TO DARWIN AND OTHERS. [1863, 



interesting, but I do not see how he got a legitimate 

 deduction from the facts given by Knight in the veg- 

 etable kingdom to his principle in the animal king- 

 dom. However, that is of small moment if the prin- 

 ciple holds. The subject is one which will naturally 

 attract much attention, and which, as you remark, has 

 philosophical bearings. I mean to bring it up, next 

 week, for discussion at our private (social) scientific 

 club in Cambridge. 



I thank you also for the good spirit in which you 

 take, as I meant them, my criticisms upon your article 

 on Species, etc. There is no progress to be made 

 upon such interesting subjects without free criticism, 

 because without it we cannot perfectly clear up our 

 own views nor impart them perfectly to others. And 

 especially, since I have so often to criticise the views 

 or writings of persons for whom I have no particular 

 regard, it is pleasant, if only for the sake of impartial- 

 ity, to criticise those for whom you have the greatest 

 regard and respect. So I particularly like it when I 

 can criticise such a near friend as J. D. Hooker or 

 Bentham, and I believe they like it, too, at least 

 Hooker, who is himself a very free critic. Of course, I 

 know very well that you will be likely to turn all the 

 points I made. The question upon which of the two 

 foundations the idea of species rests, I well know is 

 not to be settled off-hand by any bit of argument. 

 Pray take up the cudgels against me whenever an 

 occasion offers. 



As to theoretical views, you and I receive and use 

 them as means, not as ends, and expect to change 

 many of them from time to time. Such especially as 

 relate to origins and causes are the questions which 

 we ask, rather than answers that we receive ; and we 



