This book examines central themes in the thought of Rabbi Hasdai Crescas (c. 1340-1410/11), the great Catalan Jewish philosopher who contributed to the revolution of modern science and profoundly influenced Spinoza. Part I treats of Crescas' radical critique of the Aristotelian concepts of space, time, and the vacuum, and analyzes his vision of an infinite universe; it discusses his criticisms of Maimonides' proofs of God, and expounds his own proof; and it concludes with a discussion of his concept of God as infinite Love. Part II contains three essays on Crescas' strictly deterministic theory of human choice.