While Johnson charged that Milton "unhappily perplexed his poetry with his philosophy," Stephen M. Fallon argues that the relationship between Milton's philosophy and the poetry of Paradise Lost is a happy one. The author examines Milton's thought in light of the competing philosophical systems that filled the vacuum left by the repudiation of Aristotle in the seventeenth century. In what has become the classic account of Milton's animist materialism, Fallon revises our understanding of Milton's philosophical sophistication. The book offers a new interpretation of the War in Heaven in Paradise Lost as a clash of metaphysical systems, with free will hanging in the balance.