The Principles of the Most Ancient and Modern Philosophy

The only surviving philosophical work of the English philosopher Anne Conway, written in the 1670s and published after her death, first in a Latin translation in Amsterdam in 1690 and then in English in 1692. Its sources include her teacher Henry More's Platonism and the Kabbalah she studied with Francis Mercury van Helmont, who brought the book to print. Conway sets out a system of three kinds of being: God; Christ, a middle nature linking God to creation; and creatures. All creatures are, at bottom, one kind of substance, so spirit and body differ only in degree and can change into one another. This vitalist monism lets her reject both Descartes's dualism of mind and dead matter and the materialism of Hobbes and Spinoza. Creatures can change their species over time, rising or falling according to their conduct, and suffering serves to purify them, so that all creatures are finally restored. Leibniz admired the book.

It is a bold and original system by an early modern woman philosopher, offering an alternative to both dualism and materialism, and it anticipated parts of Leibniz's philosophy.