Tarski, in oral discussions, has often indicated his sympathies with nominalism. While he never accepted the ‘reism’ of Tadeusz Kotarbiński, he was certainly attracted to it in the early phase of his work. However, the set-theoretical methods that form the basis of his logical and mathematical studies compel him constantly to use the abstract and general notions that a nominalist seeks to avoid. In the absence of more extensive publications by Tarski on philosophical subjects, the conflict appears to have remained unresolved.2