  Fitch, in his (1963), does not state the argument 1—5, but instead notes that the proof of his generalized conclusion is “similar” to Church’s argument. Surprisingly, Church does not comment on the incompatibility of a Fitch-style generalization with the logical positivist doctrine that any meaningful and true proposition is in principle verifiable and hence knowable. The contemporary revival of Fitch’s argument, however, is almost entirely devoted to this issue and, more generally, to the consequences of Fitch’s argument for widely held views committed to the principle that there are no unknowable truths.