We propose to describe the faculties of the soul, and to set forth the various opinions on the subject held by both ancient and modern thinkers. DIFFERENCE BETWEEN SENSATION AND INTELLIGENCE. Aristo (there were two philosophers by this name, one a Stoic, the other an Aristotelian) attributes to the soul a perceptive faculty, which he divides into two parts. According to him, the first, called sensibility, the principle and origin of sensations, is usually kept active by some one of the sense-organs. The other, which subsists by itself, and without organs, does not bear any special name in beings devoid of reason, in whom reason does not manifest, or at least manifests only in a feeble or obscure manner; however, it is called intelligence in beings endowed with reason, among whom alone it manifests clearly. Aristo holds that sensibility acts only with the help of the sense-organs, and that intelligence does not need them to enter into activity. Why then does he subordinate both of these to a single genus, called the perceptive faculty? Both doubtless perceive, but the one perceives the sense-form of beings, while the other perceives their essence. Indeed, sensibility does not perceive the essence, but the sense-form, and the figure; it is intelligence that perceives whether the object be a man or a horse. There are, therefore, two kinds of perception that are very different from each other; sense-perception receives an impression, and applies itself to an exterior object; on the contrary, intellectual perception does not receive any impression.