All candid philosophers, in setting out on their great task of coordinating and criticizing the whole range of human thought, must often feel embarrassed by the limitations of their own knowledge. Their difficulties in dealing with scientific thought have increased very greatly during the last thirty years. For, while science has been rapidly growing more complex and abstruse, philosophers have been tending to require a more intimate knowledge of it. They are no longer interested only in scientific methods (which, it is often assumed, can be studied apart from their applications); they are beginning to find significance in particular propositions and principles. Some of these cannot be comprehended in their entirety by anyone who has not submitted himself to a training so specialized and so severe as to be almost incompatible with the width of outlook that makes the philosopher. Accordingly, philosophers have abandoned all attempts to acquire their knowledge of certain branches of science (particularly physics) from the original memoirs and expository treatises addressed to scientists; they have recourse to interpreters.