Of all the prostheses that punctuate the history of the body, the double is doubtless the most ancient. The double, however, is not properly speaking a prosthesis at all. Rather, it is an imaginary figure, like the soul, the shadow or the mirror-image, which haunts the subject as his 'other', causing him to be himself while at the same time never seeming like himself. The double haunts the subject like a subtle death, but a death forever being conjured away. Things are not always like this, however—for when the double materializes, when it becomes visible, it signifies imminent death.

In other words, the double's imaginary power and resonance—the level upon which the subject's simultaneous estrangement from himself and intimacy with himself are played out—depends upon its lack of material being, upon the fact that the double is and remains a phantasy. Everyone may dream—and everyone no doubt does dream all his life long—of a perfect duplicate, or perfect multiple copies, of his own being; but the strength of such copies lies precisely in their dream quality, and is lost as soon as any attempt is made to force dream into reality. The same is true of the (primal) scene of seduction, which is effective only so long as it is a phantasy, something re-remembered—so long as it is never real. Ours is the only period ever to have sought to exorcize this phantasy (along with others)—that is, to turn it into flesh and blood, to transform the operation of the double from a subtle interplay involving death and the Other into the bland eternity of the Same.