I am not overlooking the excuse, whose existence one must admit, for this deficiency in your previous training. There is no philosophical science of therapy which could be made practicable for your medical purpose. Neither speculative philosophy nor descriptive psychology nor that so-called experimental psychology which allies itself with the physiology of the sense organs as it is taught in the schools, is in a position to teach you anything useful concerning the relation between the physical and the psychical or to put into your hand the key to the understanding of a possible disorder of the psychic functions. Within the field of medicine, psychiatry does, it is true, occupy itself with the description of the observed psychic disorders and with their grouping into clinical symptom-pictures; but in their better hours the psychiatrists themselves doubt whether their purely descriptive account deserves the name of a science. The symptoms which constitute these clinical pictures are known neither in their origin, in their mechanism, nor in their mutual relationship. There are either no discoverable corresponding changes of the anatomical organ of the soul, or else the changes are of such a nature as to yield no enlightenment. Such psychic disturbances are open to therapeutic influence only when they can be identified as secondary phenomena of an otherwise organic affection.
Here is the gap which psychoanalysis aims to fill. It prepares to give psychiatry the omitted psychological foundation, it hopes to reveal the common basis from which, as a starting point, constant correlation of bodily and psychic disturbances becomes comprehensible. To this end, it must divorce itself from every anatomical, chemical or physiological supposition which is alien to it. It must work throughout with purely psychological therapeutic concepts, and just for that reason I fear that it will at first seem strange to you.
I will not make you, your previous training, or your mental bias share the guilt of the next difficulty. With two of its assertions, psychoanalysis offends the whole world and draws aversion upon itself. One of these assertions offends an intellectual prejudice, the other an aesthetic-moral one. Let us not think too lightly of these prejudices; they are powerful things, remnants of useful, even necessary, developments of mankind. They are retained through powerful affects, and the battle against them is a hard one.