I have to thank you very much for your two letters, and also for the enclosures from [Moulton], which I now return.¹ The latter convey exactly the criticism that I should have expected from [Moulton], for while writing my essay on Theism I had several conversations with him upon the subject of Spencer’s writings, and so know exactly what he thinks of them.² But in none of these conversations could I get at anything more definite than is conveyed by the returned letters. In no point of any importance did he make it clear to me that Spencer was wrong, and the only result of our conversation was to show me that in [Moulton’s] opinion it was only my ignorance of mathematics that prevented me from seeing that Mr. Spencer is merely a ‘word philosopher.’ Upon which opinion I reflected, and still reflect, that the mathematicians must be a singularly happy race, seeing that they alone of men are competent to think about the facts of the cosmos. And this reflection becomes still more startling when supplemented by another, viz. that although one may not know any mathematics, everybody knows what mathematics are: they are the sciences of number and measurement, and as such, one is at a loss to perceive why they should be so essentially necessary to enable a man to think fairly and well upon other subjects. But it is, as you once said, that when a man is to be killed by the sword mathematical, he must not have the satisfaction of even knowing how he is killed. Of course, in a general way I quite understand and agree with [Moulton] that Spencer has done but little service to science. But I believe that he has done great service to thinking, and all the mathematicians in the world would not convince me to the contrary, even though they should all deliver their judgment with the magnificent authority of a [Moulton].

Coming now to the diagram, I am much obliged to you for your suggestions. The ‘Descent of Man,’ with all its references upon the subject, and also your paper on the ‘Baby,’ were read, and the results embodied in the diagram, so I am very glad you did not take the needless trouble of consulting these works.³ By ‘Love’ I intend to denote the complex emotion (dependent on the representative faculties) which, having been so lately smitten myself, I am perhaps inclined to place in too exalted a position. But you did not observe that I placed ‘Parental Affection’ and ‘Social Feeling’ very much lower down.⁴

In my essay I carefully explain the two cases of Drosera and Dionæa as being the best hitherto observed for my purpose in establishing the principle of discrimination among stimuli, as a principle displayed by non-nervous tissues.⁵