Psychiatry is, more than others, an empirical science. Whatever we know about it we have learned by experience and observation. As I have repeatedly insisted, neither in somatic nor in psychical medicine are there any sharp boundaries between health and disease. In reference to the body, “feeling well” is the chief mark of health. Everybody who is sick knows it. Connected with the majority of diseases there are positive pains, in consequence of which those who are taken ill send for the doctor. Pain has rightly been called the sentinel of health; but with the mind it is otherwise. Here there is no such connection between health and feeling well. The illness gives no pain, at least not directly; and the patient is in very little condition to say whether he is well or not. On the contrary, the consciousness of being deranged is recognized as the most marked symptom of convalescence. The question has here to be decided in quite other ways. Disease is not an entity, and no precise definition can be given of it. The chief point upon which the decision must turn is the person’s ability to do his duties to society.

We have learned by experience that there are certain typically recurring forms of a psychical process in which a disorder of self-consciousness has taken place, so that the persons affected were deprived of their self-control. We have become acquainted with well-marked cases in which a general decay of the mental powers commenced; and this has gone on until the capacity of the patients for business has sunk to nothing, etc. In this purely experimental way we have come to recognize classes of mental diseases which are marked by certain phenomena and by a certain course.

The next step in the progress of science was the comparison of the psychological conditions of those who were undoubtedly insane with mentally sane men. Here we had a right to the premises that on the one side we had minds mentally sound, and on the other minds mentally deranged. Having studied the psychological distinctions between the two, psychiatrists came to recognize the so-called symptoms of insanity.

It is important to remark that, although the aggregate of the symptoms constitutes the disease, yet it was not the symptoms which primarily presented themselves to our recognition. On the contrary, we first attained it by the study of the single elements of the diseases. For example, in early times hallucinations were explained in all sorts of mystical ways, as seeing ghosts, divine visions, suggestions of the devil, etc.; but by the study of mental diseases psychiatrists came to recognize that in such cases hallucinations are extraordinarily frequent. They thus become accustomed to consider the occurrence of hallucinations as in every case a morbid symptom. In fact, it became apparent that wherever there were illusions of the senses, as a rule, a mental disorder could be made out.