Spinoza was born to a family of Marrano Jews that emigrated from Portugal to the Netherlands in order to return to Judaism. Spinoza's first encounter with philosophy was most probably through the writings of Maimonides. By the age of fourteen Spinoza left the school of the Jewish community and entered into his family's commercial business. A few years later, Spinoza began studying Latin and came into contact with the circles of freethinkers and the new Cartesians. In July 1656, Spinoza was excommunicated by the Sephardic Jewish community of Amsterdam for reasons still unclear. In the following years, Spinoza deepened his study of Descartes and other philosophers, and in 1663, upon the request of students and friends, he published his book on Descartes’ Principles of Philosophy, in which he presented the first two parts of the Principles in a geometrical manner. Already in this book one can discern a sharp critique of Descartes, a critique that became bolder and more explicit in his later works.

Descartes’ philosophy had a decisive influence on Spinoza. Essentially, Cartesian philosophy provided most of the philosophical vocabulary for Spinoza's own system. But despite Leibniz's claim that Spinoza “only cultivated certain seeds in the philosophy of Descartes” (G 2.563), Spinoza himself seemed to be deeply disappointed by what he considered to be Descartes’ unprincipled compromises and tendency to accommodate popular religious and philosophical beliefs.

In the Principles, Descartes offers an apparently disjunctive definition of substance. A substance for Descartes is that which depends either on nothing else for its existence (God) or only on God's concurrence for its existence (created substances) (AT VIIIA 24, CSM I 210). Spinoza rejects this compromise, which allows for finite substances, defining a substance as “what is in itself and is conceived through itself”– that is, a being that is ontologically and conceptually independent (E1d3). From this definition, Spinoza infers that if anything is a substance, it cannot be caused by any other thing (E1p6), it exists necessarily (E1p7), and it is necessarily infinite (E1p8).