The Viscountess Anne Conway enjoys a more distinguished reputation as a metaphysician than her contemporary Margaret Cavendish. In her own time, Conway was praised as ‘a woman learned beyond her sex’; in the nineteenth century, James Crossley regarded her as ‘the profoundest and most learned of the female metaphysical writers of England’; and in a recent article, Sarah Hutton describes Conway as ‘the most important’ woman philosopher in seventeenth-century England. These accolades are well deserved. Unlike Cavendish, Conway presents concise and systematic arguments for her metaphysical views, and her ideas are developed from clearly defined philosophical and theological principles. While Cavendish's works seem to have been ignored by her peers, Conway's system was admired by no less a philosopher than Gottfried Wilhelm Leibniz.

Yet, in outward appearances, there are strong parallels between the ontological theories of Conway and Cavendish. Conway undoubtedly knew about Cavendish's writings through her correspondence with Henry More. In fact, More encouraged Conway to write a response to the Philosophical Letters. But as far as we know, Conway's only surviving work is The Principles of the Most Ancient and Modern Philosophy (first published in Latin in 1690). In this treatise, her principal target is Cartesianism, but like Cavendish, she also takes a critical attitude toward Henry More's concept of the soul and his dualist theory of soul–body relations. The other main targets of the Principles are Spinoza and Hobbes.