Similarly, when, as in the sculpture of Kiki Smith and the painting of Julie Heffernan, the naked body is a prop for the isolated self -- the instrument of an allegory of narcissistic injury and vulnerability, at once ideological and personal in import -- it makes no sense to speak of nakedness or nudity as its essence. And when, as in Joel Peter Witkins' biologically grotesque nudes and Lucas Samaras' emotionally grotesque nudes, the body seems to have imploded, monstrousness has made the distinction between nakedness and nudity irrelevant.

In modern art, the distinction between naked and nude has lost the weight it had back when representing the body was a moral act: the transcendentalized nude, with its perfect body, was a symbol of goodness and beauty -- ideals to be striven for -- while the realistically naked body, with all its blemishes, imperfections and grossness, was inherently immoral -- the ugly body of the fallen, sinful Adam or Eve, the antithesis of the saved soul rising to heaven.

The problem embodied in the traditional tension between nakedness and nudity was the mystery of the transformation of the one into the other, which was a religious mystery, for the metamorphosis of the profane into the sacred was a miraculous conversion. One could change one's wretched, hideous body -- like that of the crucified Christ in Grünewald's Isenheim Altar -- to a luminous, immaterial, sublime body -- like that of the resurrected Christ Grünewald also depicts -- by a revelatory leap of faith. It is this basic spiritual change that is embodied in the difference between nakedness and nudity: the naked body conveys the state of the soul before the change, the nude body conveys its condition afterward.

The realistically naked body is the soul in mortal danger, the ideal nude body shows that it has become immortal -- overcome death. When Albrecht Dürer created subliminally ideal yet empirically accurate bodies by giving them harmonious proportions, he was in effect articulating the mystery of mysteries: humanity would be saved in all its physical particularity if it only had faith in God, confirming that his physical creation was inherently perfect.

Nonetheless, the bodies, whatever their spiritual import -- whether excruciatingly actual or tranquilly ideal, whether frail and vulgar or heroic to the extent of seeming invulnerable -- are rendered without clothing. One speaks of the naked truth, suggesting that the state of nakedness has always been emblematic of truthfulness. When Bernini presents the truth as a naked woman or Michelangelo sculpts a naked David -- quite unlike Donatello's clothed David -- or when the figures in medieval hell are presented unclothed, presumably the truth is being stated: the uncompromising truth of existence symbolized by the body stripped bare.

It is the nakedness that tells the shocking human truth -- the perverse truth -- in Larry Clark's photograph of a young woman shooting up in the company of another young woman and an immature boy (with a mature erection), not the fact of her drug addiction.

Without their nakedness, Hans Bellmer's and Cindy Sherman's grotesquely fragmented mannequins would seem like innocent freaks rather than morbidly truthful -- less of a confrontation with the emotional truth and more like a manufactured mirage, which is the way most of the mannequins produced by the Surrealists look. Without their nakedness, they would not transcend their artificiality, and would certainly be less provocative. We know that Alberto Giacometti's figures must be naked -- stripped bare -- because they seem existentially authentic and true to themselves, and we experience Paul Delvaux's women as confronting us with the truth of sexual desire because they are naked.

Freud speaks of what happens when we take off our clothes at the end of the day: we regress. Implicitly naked when we sleep, whatever we may in fact wear, we are once again infants -- emotionally naked as the day we were born. I think the artistically successful nude has one basic purpose, whatever other fantasies it may serve: to remind us, unconsciously, of what it was like to be born helpless and unprotected -- to have experienced the trauma of birth and the trauma of total dependence.

The representation of the mature body often tries to hide the primitive emotional truth evoked by nakedness -- the vulnerable sense of immaturity we all unconsciously feel when we are naked -- by suggesting its sexual potential, but so long as there is fidelity to the lived body, which involves a sense of the way time is experienced through the body, then the infantile truth it implies will be evoked.

The German language distinguishes between Leib and Körper -- the lived body and the body as a thing. To use Erich Fromm's distinction, it is the difference between the body in the mode of being and the body in the mode of having. Many artists render the body as a thing -- in effect a corpse -- that happens to be the site of pleasure and pain, which makes it seem physically alive if not emotionally deep. The best representations of the nude convey a sense that the body is inherently alive, independent of the joy or suffering it may bring. I think Gustave Courbet's female nudes do this with particular brilliance, putting to shame Edouard Manet's thing-like naked females.

The reason that Sally Mann's photographs of unclothed children shock adults is because they instantly identify with them, which means to re-experience the infantile state of vulnerability and dependence their nakedness represents. Nakedness is disturbing, however much we may sexualize it, because it unconsciously reminds us of the day we were born, thus reminding us of our limitations and death. There is no such thing as innocent nakedness -- not a baby's or a child's or an adult's -- because all nakedness restores us to the womb and foreshadows the grave, and the vicissitudes of the self during its passage from the one to the other. It is they that the best nudes insinuate into our psyches.

This means, paradoxically, that the nudes of Bellmer and Sherman are among the very best, for they are constructions of infantile part objects -- representations of the body in which its wholeness is not convincing, which is why it does not seem adequately organic -- suggesting that the body exists as much in name as in fact. We have seen this already in a number of Picasso's nudes, where the body is not simply distorted as in the German Expressionists -- stretched to its expressive limits while maintaining its physical integrity -- but a composite of incommensurate parts that are arbitrarily reconciled, forming a bizarre totality rather than a unified whole. Picasso is clearly the master of absolute grotesqueness -- radical ugliness, nakedly physical and emotional. Thus, it seems that in the best 20th-century art the nude is the vehicle for an infantile vision of the "broken" body -- a regressive vision that ironically makes for a progressive "avant-garde" or at least broadly "modern" look.

This continues to be the case, as the grotesque (if more integral) nudes of Lucian Freud and Jenny Saville suggest. The modern experience of nakedness as grotesque suggests that insight into the infantile depths of the psyche comes at the high price of emotional stability, for the physical fragments out of which Picasso, Bellmer and Sherman construct the nude are also the fragments of the self. The grotesque nude is inherently unstable -- a poorly reconstructed Humpty Dumpty that is liable to crumble into chaos again, at any moment.

The body is, as Sigmund Freud says, the first ego, and when the body disintegrates into a heap of fragments so does the ego. This is perhaps what makes the modern nude especially fascinating: it signals the haphazard, inexact way the modern self is constructed -- its precarious condition and lack of foundation, behind its concern to be "progressive."

Thus what Yeats calls the modern fascination with what's difficult has discovered that the naked body, with all the raw, primitive feelings it arouses, is the most difficult, unfamiliar, uncanny, slippery of all objects, however ordinary it may seem to the naked eye.