'Finding only a vague notion of progress from lower to higher, he [Spencer] has affixed the specific meaning to the word higher of which I gave an account, defining the processes by which this progress is effected. He has, moreover, formed the conception of evolution as the subject of general propositions applicable to all natural processes, a conception which serves as the basis of a complete system of philosophy. In particular, he has applied this theory to the evolution of mind, developing the complete accordance between the laws of mental growth and of the growth of other organic functions. In fact, even if the two points which I put forward as my own - viz. the formal application of the biological method to a certain special problem, and the biological law which serves as a partial solution of it - have not before been explicitly developed (and of this I am not sure), yet they are consequences so immediate of the general theory that in any case the credit of them should entirely belong to the philosopher on whose domains I have unwittingly trespassed. The mistake, of course, affects me only, and could in no way injure the fame of one whose philosophical position is so high and so assured.' (72-73)