Tarski's postscript (Ps) to the second, German edition of his famous work on the concept of truth (Wb, for "Wahrheitsbegriff"), began by a recantation about the theory of semantical categories. In Wb he had unreservedly supported this theory, in Ps he rejected it. But there is strong evidence that something deeper had happened, beyond this avowed change of opinion and irreducible to it, something unavowed, perhaps unthought. I identify this deeper change as an abandonment of the universalism inherited from the founding fathers of modern logic, to which Tarski had previously remained faithful. I argue that this abandonment was, beyond all mathematical proof, a matter for philosophy.