Charles Peirce had a flair for asking fruitful questions and for proposing answers that did not block the way of inquiry. Typical examples occur in his philosophy of science where he raises issues that are still very much alive. They include such items as the nature and conditions of scientific progress, the grounds of human success in formulating theories, the completability of scientific knowledge, and the limits imposed by the economy of research. Because these are living issues, Peirce's ideas about them invite examination as if he were our philosophical contemporary. Nicholas Rescher so examines them in his compact, timely book. His treatment is sympathetic but by no means uncritical, as might have been expected in view of the similarities and differences between his own position of methodological pragmatism and the pragmaticism of Peirce. The ensuing discussion thus seems to me worth looking at in a bit of detail.

Relative Identity contains a sustained attack on the classical or absolute theory of identity and a defense of a non-classical or relative theory of identity. According to the absolute theory of identity each thing is identical with itself and with nothing other than itself. The fundamental principle of this theory is Leibniz' Law:

From (LL) a variety of characteristic principles about identity can be derived, including The Indiscernibility of Identicals, The Identity of Indiscernibles, and the symmetry, reflexivity, and transitivity of identity.