My reply to this question is clear: it is the motor manifestations which are essential. In other words, what are called agreeable or painful states only constitute the superficial part of the life of feeling, of which the deep element consists in tendencies, appetites, needs, desires, translated into movements. Most classical treatises (and even some others) say that sensibility is the faculty of experiencing pleasure and pain. I should say, using the same terminology, that sensibility is the faculty of tending or desiring, and _consequently_ of experiencing pleasure and pain. There is nothing mysterious in the tendency; it is a movement or an arrest of movement in the nascent stage. I employ this word “tendency” as synonymous with needs, appetites, instincts, inclinations, desires; it is the generic term of which the others are varieties; it has the advantage over them of embracing at the same time both the psychological and physiological aspects of the phenomenon. All the tendencies suppose a motor innervation; they translate the needs of the individual, whatever they may be, physical or mental; the basis, the root of the affective life is in them, not in the consciousness of pleasure and pain which accompanies them according as they are satisfied or opposed. These agreeable or painful states are only signs and indications; and just as symptoms reveal to us the existence of a disease, and not its essential nature, which must be sought in the hidden lesions of the tissues, organs, and functions, so pleasure and pain are only _effects_ which must guide us in the search and determination of causes hidden in the region of the instincts. If the contrary opinion has generally prevailed, and priority been accorded to the study of agreeable and painful manifestations considered as the essential element in the emotional life and serving to define it, that is the result of a bad method, of an exclusive faith in the evidence of consciousness, of a common illusion which consists in believing that the conscious portion of an event is its principal portion, but especially the consequence of the radically false idea that the bodily phenomena which accompany all states of feeling are factors that are negligible and external, foreign to psychology, and without interest for it. For the present what has just been said is only an affirmation; the proofs will come later, and will occupy the whole of this book; at the outset it is only necessary to indicate clearly the position taken up. We may now follow the evolution of the life of feeling in its chief stages, which are—pre-conscious sensibility, the appearance of the primitive emotions, their transformation either into complex and abstract emotions or into that stable and chronic state which constitutes the passions. I.