Originally published in 1972, Medieval Logic and Metaphysics shows how formal logic can be used in the clarification of philosophical problems. An elementary exposition of Leśniewski's Onotology, an important system of contemporary logic, is followed by studies of central philosophical themes such as Negation and Non-being, Essence and Existence, Meaning and Reference, Part and Whole. Philosophers and theologians discussed include St Anselm, St Thomas Aquinas, Abelard, Ockham, Scotus, Hume and Russell.