Why have not these, also, separated off and set up for themselves?
Is it more difficult to work in these fields than in others?
and, if so, what reason can be assigned for the fact?
Take psychology as an instance.

How does it happen that the physicist calmly develops his doctrine without finding it necessary to make his bow to philosophy at all, while the psychologist is at pains to explain that his book is to treat psychology as "a natural science," and will avoid metaphysics as much as possible?
For centuries men have been interested in the phenomena of the human mind.

Can anything be more open to observation than what passes in a man's own consciousness?
Why, then, should the science of psychology lag behind?
and why these endless disputes as to whether it can really be treated as a "natural science" at all?
Again.

May we assume that, because certain disciplines have taken a position of relative independence, therefore all the rest of the field will surely come to be divided up in the same way, and that there will be many special sciences, but no such thing as philosophy?
It is hasty to assume this on no better evidence than that which has so far been presented.

Before making up one's mind upon this point, one should take a careful look at the problems with which the philosopher occupies himself.
A complete answer to the questions raised above can only be given in the course of the book, where the main problems of philosophy are discussed, and the several philosophical sciences are taken up and examined.