Plato, in his Symposium, makes one of the guests assert that there are two Aphrodites, whom he calls Celestial and Vulgar, or, to give them their later titles, Venus Coelestis and Venus Naturalis; and because it symbolized a deep-seated human feeling, this passing allusion was never forgotten. It became an axiom of medieval and Renaissance philosophy. It is the justification of the female nude. Since the earliest times the obsessive, unreasonable nature of physical desire has sought relief in images, and to give these linages a form by which Venus may cease to be vulgar and become celestial has been one of the recurring aims of European art. The means employed have been symmetry, measurement, and the principle of subordination, all refining upon the personal affections of individual artists. But perhaps this purification of Venus could not have taken place had not some abstract notion of the female body been present in the Mediterranean mind from the first. Prehistoric images of women are of two kinds, the bulging statuettes from paleolithic caves, which emphasize the female attributes till they are little more than symbols of fertility and the marble dolls of the Cyclades, in which already the unruly human body has undergone a geometrical discipline. Following Plato's example, we might call them the Vegetable and the Crystalline Aphrodite. These two basic conceptions never quite disappear, but since art involves the application of laws, the distinction between the two Aphrodites grows very slight; and even when most unlike one another they partake of each other's characters. Botticelli's Venus "born of the crystalline sea of thought and its eternity" has a piercing strain of sensuality; Rubens' Venus, a cornucopia of vegetable abundance, still aspires to the idea. 
Clark, Kenneth. The Nude: A Study in Ideal Form. Bollingen Series 35.2. New York: Pantheon Books, 1956.
Last modified 16 February 2007