Of the mental functions, whether representative images, perceptions, or volitions, a part are referred to body (to parts of our own body, often also to external objects), and produced by the body (by the animal spirits and, generally, by the nerves as well), while the rest find both object and cause in the soul. Intermediate between the two classes stand those acts of the will which are caused by the soul, but which relate to the body, _e.g._, when I resolve to walk or leap; and, what is more important, the _passions_, which relate to the soul itself, but which are called forth, sustained, and intensified by certain motions of the animal spirits. Since only those beings which consist of a body as well as a soul are capable of the passions, these are specifically human phenomena. These affections, though very numerous, may be reduced to a few simple or primary ones, of which the rest are mere specializations or combinations. Descartes enumerates six primitive passions (which number Spinoza afterward reduced one-half)--_admiratio, amor et odium, cupiditas (désir), gaudium et tristitia_. The first and the fourth have no opposites, the former being neither positive nor negative, and the latter both at once. Wonder, which includes under it esteem and contempt, signifies interest in an object which neither attracts us by its utility nor repels us by its hurtfulness, and yet does not leave us indifferent. It is aroused by the powerful or surprising impression made by the extraordinary, the rare, the unexpected. Love seeks to appropriate that which is profitable; hate, to ward off that which is harmful, to destroy that which is hostile. Desire or longing looks with hope or fear to the future. When that which is feared or hoped for has come to pass, joy and grief come in, which relate to existing good and evil, as desire relates to those to come.