If, leaving aside the endless enumeration of the kinds of fear and their description, we seek—for this is the task incumbent on psychology—to determine their derivation from normal fear, and the causes which excite them, we enter an almost unexplored region and pass from riches to indigence. As far as concerns their psychological origin, _i.e._, the determination of the normal type from which they are deviations, I propose reducing them to two groups. The first is directly connected with fear, and includes all manifestations implying in any degree whatever the fear of pain, from that of a fall or the prick of a needle to that of illness or death. The second is directly connected with disgust, and seems to me to include the forms which have sometimes been called _pseudophobia_ (Gélineau). Such are the fear of contact, the horror of blood, and of innocuous animals, and many strange and causeless aversions. Let us remark, furthermore, that fear and disgust have a common basis, being both instruments of protection or defence. The first is the defensive-conservative instinct of the relative life, the second the defensive-conservative instinct of the organic life. As both have a common basis of aversion, they show themselves in equivalent ways: fear by withdrawal, departure, flight; disgust by vomiting or nausea. The reflexes of disgust are the succedanea of flight; the organism cannot escape by movement in space from the repugnant body which it has taken into itself, and goes through a movement of expulsion instead. After having traced back all morbid fears to two sources—which may indeed be reduced to one—we have to seek for their causes. One very general cause, with which most authors content themselves, is degeneracy. I shall speak of this elsewhere (see Conclusion); but as it is constantly brought in to explain the most dissimilar manifestations, it assumes such a general character that it becomes necessary to supplement it. Let us then, if any importance is attached to this, assume degeneracy as the soil on which morbid fears spring up and multiply; then let us seek the complementary causes, which are less vague and nearer to the facts. I would propose three such.