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- 
m. 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 m 
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 
