The distinction between essence (essentia) and existence (existentia) plays a major role in Spinoza’s metaphysics. Although the distinction did not originate with Avicenna, it is primarily through Avicenna’s influence that it became widespread, if not ubiquitous, in both Jewish and Christian medieval philosophy (e.g., Ogden 2021). Spinoza was clearly familiar with this important distinction through his study of Maimonides, Crescas, and Descartes, and it is particularly useful to examine Spinoza’s employment of the distinction in contrast to Descartes’s. In the Meditations, Descartes relies on the distinction in a proof of God’s existence, and in his exploration of the essence of material things (both in the Fifth Meditation). For Descartes, Extension – which is the principal attribute of all bodies – is separable from existence. For this reason, Descartes thought he could provide an adequate account of Extension independently of the question of whether bodies exist (the existence of bodies being proved only in the Sixth Meditation). The same considerations also apply to Descartes’s understanding of minds, finite thinking substances, which do not exist just by virtue of their nature, but rather by virtue of the cause which created them: God.