Is metaphysics possible? This book argues that the greatest threat to its viability derives from a self-destructive formalism. If what is essential to the nature of physical entities are the properties they have in common (as formalism holds), the inevitable result will be a reductionist collapse--leaving only "being" or physical "matter" or some other underlying ground. In Essential Difference, James Blachowicz first constructs a one-to-one historical parallel between the modern crisis surrounding formalism (Hume/Kant/Hegel) and the ancient version (Parmenides/Plato/Aristotle), focusing on the principles of differentiation and individuation that underlie Aristotle's and Hegel's antireductionist programs. He then proposes a contemporary metaphysical theory of emergence in the context of recent philosophy of science. This theory, founded on the principle of the nonderivability of actual states from possible states, holds that the differences among physical, biological, and mental phenomena are essential to any metaphysics. Essential Difference is the only focused treatment of this problem and is itself essential for any understanding of the nature of metaphysics.