Truth cannot be defined or tested by agreement with 'the world'; for not only do truths differ for different worlds but the nature of agreement between a world apart from it is notoriously nebulous.

Simons (1987) and Casati and Varzi (1999) show that the calculus of individuals can be grounded in either in a bit of set theory or in monadic predicates schematically employed. "The Calculus of Individuals and Its Uses" (with Henry S. OEG-0-9-310283-3721 (010) 1972.