Leibniz's Principle of Identity of Indiscernibles

Gonzalo Rodriguez-Pereyra presents a new study of Leibniz's Principle of the Identity of Indiscernibles--a principle which rules out numerically distinct but perfectly similar things. He explores Leibniz's definition of the Principle, evaluates his arguments for and from it, and concludes that it was central but inessential to Leibniz's philosophy.