If you'll permit me to use one of those formulas which come to me as I write my notes, human life could be defined as a calculus in which zero was irrational. This formula is just an image, a mathematical metaphor. When I say ``irrational,'' I'm referring not to some unfathomable emotional state but precisely to what is called an imaginary number. The square root of minus one doesn't correspond to anything that is subject to our intuition, anything real -- in the mathematical sense of the term -- and yet, it must be conserved, along with its full function. [Lacan (1977, 28-29), seminar originally given in 1959.]