This work investigates how the concept of substance serves as the foundational metaphysical pillar for the philosophical systems of Descartes, Spinoza, and Leibniz. R. S. Woolhouse, a scholar of early modern philosophy, examines the divergent ways these thinkers defined the nature of reality and existence. By analyzing their primary texts, the author constructs a comparative framework that highlights the transition from Cartesian dualism to the monism of Spinoza and the pluralistic monadology of Leibniz. The book argues that the definition of substance is the key to understanding the internal logic and contradictions of seventeenth-century rationalism.

Scholars and students of philosophy frequently cite this text as a rigorous and clear introduction to the complex metaphysical debates of the seventeenth century. Experts highlight the book's ability to synthesize dense technical arguments into a coherent narrative for those familiar with the history of Western philosophy.