 “Set theory is wrong” and nonsensical (PR §174), says Wittgenstein, because it presupposes a fictitious symbolism of infinite signs (PG 469) instead of an actual symbolism with finite signs. The grand intimation of set theory, which begins with “Dirichlet’s concept of a function” (WVC 102–03), is that we can in principle represent an infinite set by an enumeration, but because of human or physical limitations, we will instead describe it intensionally. But, says Wittgenstein, “[t]here can’t be possibility and actuality in mathematics”, for mathematics is an actual calculus, which “is concerned only with the signs with which it actually operates” (PG 469). As Wittgenstein puts it at (PR §159), the fact that “we can’t describe mathematics, we can only do it” in and “of itself abolishes every ‘set theory’”.