Kenneth Clark opens his classic study, The Nude: A Study in Ideal Form, by pointing out that
The English language, with its elaborate generosity, distinguishes between the naked and the nude. To be naked is to be deprived of our clothes, and the word implies some of the embarrassment most of us feel in that condition. The word "nude," on the other hand, carries, in educated usage, no uncomfortable overtone. The vague image it projects into the mind is not of a huddled and defenseless body, but of a balanced, prosperous, and confident body: the body re-formed. In fact, the word was forced into our vocabulary by critics of the early eighteenth century to persuade the artless islanders [of the UK] that, in countries where painting and sculpture were practiced and valued as they should be, the naked human body was the central subject of art. 
Clark continues that "in the greatest age of painting, the nude inspired the greatest works; and even when it ceased to be a compulsive subject it held its position as an academic exercise and a demonstration of mastery" (3). It did so, he explains because the nude as a conceptual and artistic category always involved the notion of an ideal abstracted from the reality we confront in our everyday lives. As such, we may add, the nude in art plays a role similar to that of the hero in epic: it provides the means and occasion to figure forth what a particular society takes to be greatest excellence. The nude, therefore, "is not the subject of art, but a form of art" (5), in part because "The body is not one of those subjects which can be made into art by direct transcription — like a tiger or a snowy landscape. . . . We do not wish to imitate; we wish to perfect" (5-6) — an idea, like so many others, perhaps first formulated by Aristotle "with his usual deceptive simplicity. 'Art,' he says, 'completes what nature cannot bring to a finish. The artist gives us knowledge of nature's unrealized ends.' A great many assumptions underlie this statement, the chief of which is that everything has an ideal form of which the phenomena of experience are more or less corrupted replicas. . . . Every time we criticize a figure, saying that a neck is too long, hips are too wide or breasts too small, we are admitting, in quite concrete terms, the existence of ideal beauty" (12-13).
This nude as idea form can embody not only "biological needs" but also the harmony of classical art, the energy and ecstasy of romanticism, and the pathos of the sufferings of Christ and His martyrs, and "when we see the beautiful results of such embodiments, it must seem as if the nude as a means of expression is of universal and eternal value. But we know this to be historically untrue" (9).
Clark, Kenneth. The Nude: A Study in Ideal Form. Bollingen Series 35.2. New York: Pantheon Books, 1956.
Last modified 16 February 2007