Which parts of Descartes’s philosophy did Spinoza reject?

While Benedict de Spinoza’s work was deeply influenced by René Descartes, he rejected key elements of Cartesian metaphysics that he believed rendered the world unintelligible. Specifically, Spinoza rejected three central features of Descartes’s philosophy:1

• The transcendence of God: Unlike Descartes, who posited a transcendent deity, Spinoza argued for a pantheistic view where God is not separate from the world but is the single, infinite substance of which all things are modes.21
• Mind-body dualism: Spinoza rejected the conception of the mind as a distinct "mental substance" that causally interacts with matter. Instead, he proposed a monistic theory where mind and body are simply different attributes of the same underlying substance.13
• Free will: Spinoza rejected the ascription of free will to both God and human beings, viewing such a doctrine as incompatible with a rational, deterministic understanding of nature.1

By rejecting these dualistic and transcendent foundations, Spinoza developed a monistic system that he viewed as the logical outcome of Cartesian principles.1