This book investigates the metaphysical distinction between the essential and accidental properties of individuals. Penelope Mackie, a philosopher specializing in metaphysics, evaluates the criteria by which we determine what makes an object or person what it is. She critiques prevailing theories in contemporary analytic philosophy to propose a framework she terms Minimalist Essentialism, which seeks to refine our understanding of identity across possible worlds.

Experts in the field of analytic philosophy recognize this work as a rigorous contribution to the ongoing debate regarding modal properties. Readers frequently note the technical density of the prose, which assumes a foundational knowledge of contemporary metaphysical discourse.