Again. The psychologist speaks of the relation of mind and body. Some psychologists incline to be parallelists, some are warm advocates of interactionism. Now, any theory of the relation of mind to body must depend on observation ultimately. If we had not direct experience of a relation between the physical and the mental somewhere, no hypothesis on the subject would ever have emerged. But our experiences are not perfectly clear and unequivocal to us. Their significance does not seem to be easily grasped. To comprehend it one is forced to that reflective examination of experience which is characteristic of the philosopher (Chapter IX). Here it may again be said: Leave the matter to the meta-physician and go on with your psychological work. I answer: The psychologist is not in the same position as the botanist or the zooelogist. He is studying mind in its relation to body. It cannot but be unsatisfactory to him to leave that relation wholly vague; and, as a matter of fact, he usually takes up with one theory or another. We have seen (section 36) that he may easily adopt a theory that leads him to overlook the great difference between physical phenomena and mental phenomena, and to treat them as though they were the same. This one may do in spite of all that introspection has to say about the gulf that separates them. Psychology is, then, very properly classed among the philosophical sciences. The psychologist is not sufficiently sure of his materials to be able to dispense with reflective thought, in many parts of his field. Some day there may come to be a consensus of opinion touching fundamental facts, and the science may become more independent. A beaten track may be attained; but that has not yet been done. 70. THE DOUBLE AFFILIATION OF PSYCHOLOGY.--In spite of what has been said above, we must not forget that psychology is a _relatively_ independent science. One may be a useful psychologist without knowing much about philosophy. As in logic it is possible to write a text-book not greatly different in spirit and method from text-books concerned with the sciences not classed as philosophical, so it is possible to make a useful study of mental phenomena without entering upon metaphysical analyses. In science, as in common life, we can _use_ concepts without subjecting them to careful analysis. Thus, our common experience reveals that mind and body are connected. We may, for a specific purpose, leave the _nature_ of this connection vague, and may pay careful attention to the physiological conditions of mental phenomena, studying in detail the senses and the nervous system. We may, further, endeavor to render our knowledge of mental phenomena more full and accurate by experimentation. In doing this we may be compelled to make use of elaborate apparatus. Of such mechanical aids to investigation our psychological laboratories are full.