I objected that the principle of fecundity, far from being self-consistent, might be so ontologically prodigal that it actually leads to contradiction. It’s like the set of all sets—which, being a set, has to contain itself. But if some sets contain themselves, one can also consider the set of all sets that don’t contain themselves. Call this set R. Now ask, Does R contain itself? If it does, then by definition it doesn’t; and if it doesn’t, then by definition it does. Contradiction! (Weinberg, of course, immediately recognized this as Russell’s paradox.) The fecundity principle, I claimed,
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