Entering the lion's den with trepidation, this particular Daniel appears to have escaped the wrath of philosophers with fewer wounds than might have been anticipated. I have never shared the belief, endemic among many scientists, that philosophy has nothing to teach us; the evils wrought by a wrong philosophy of science are too obvious for one to make such lighthearted comments, which indicate little but that the writer is self-taught and a good example of the horrors of unskilled labour. Nevertheless, my contribution was not intended to be the kind of composition that a professional philosopher might have put forward; I tried as best I could to join together philosophy of science, history of science, sociology of science, and psychology of science and to illustrate my conclusions by reference to some of my own studies. This was perhaps too ambitious an undertaking for a chapter and in due course may lead to the preparation of a book; however, the kindly welcome my efforts have received from three professional philosophers encourages me to believe that some, at least, of the major points I was trying to make may have been in the right direction.