for instance, those originating in the body, such as the desire for nourishment, namely hunger and thirst, and a separate kind of desire answering to each kind of nourishment; and the desires connected with taste and sex and sensations of touch in general; and those of smell, hearing, and vision. Rational desires are those which we are induced to have; there are many things we desire to see or get because we have been told of them and induced to believe them good. Western philosophers In Passions of the Soul, René Descartes writes of the passion of desire as an agitation of the soul that projects desire, for what it represents as agreeable, into the future. Desire in Immanuel Kant can represent things that are absent and not only objects at hand. Desire is also the preservation of objects already present, as well as the desire that certain effects not appear, that what affects one adversely be curtailed and prevented in the future. Moral and temporal values attach to desire in that objects which enhance one's future are considered more desirable than those that do not, and it introduces the possibility, or even necessity, of postponing desire in anticipation of some future event, anticipating Sigmund Freud's text Beyond the Pleasure Principle. See also, the pleasure principle in psychology. In his Ethics, Baruch Spinoza declares desire to be "the very essence of man," in the "Definitions of the Affects" at the end of Part III. An early example of desire as an ontological principle, it applies to all things or "modes" in the world, each of which has a particular vital "striving" (sometimes expressed with the Latin "conatus") to persist in existence (Part III, Proposition 7). Different striving beings have different levels of power, depending on their capacity to persevere in being. Affects, or emotions which are divided into the joyful and the sad, alter our level of power or striving: joy is a passage "from a lesser to a greater perfection" or degree of power (III Prop. 11 Schol.), just as sadness is the opposite. Desire, qualified by the imagination and the intellect, is an attempt to maximize power, to "strive to imagine those things that increase or aid the body's power of acting." (III Prop. 12). Spinoza ends the Ethics by a proposition that both moral virtue and spiritual blessedness are a direct result of essential power to exist,