Spinoza’s “Principles of Cartesian Philosophy”

 

Spinoza’s “Principles of Cartesian Philosophy” is a comprehensive exposition of René Descartes' philosophical system, yet it is also a critical engagement with Cartesian thought. Spinoza wrote this work in 1663, as a guide to the core ideas of Descartes, intending to make them more accessible to students. However, while Spinoza presents Descartes' philosophy faithfully, he also begins to incorporate and hint at his own philosophical ideas, which later culminated in his Ethics. Spinoza’s approach in this work is twofold: he elucidates Descartes’ principles of philosophy, including metaphysics, physics, and epistemology, while subtly questioning and reinterpreting these principles in ways that prefigure his own system of thought.

Descartes’ philosophy begins with doubt as a method of arriving at certain knowledge. Descartes famously advocates for radical doubt — doubting everything that can be doubted, in order to discover what cannot be doubted. This method, known as methodological skepticism, leads to Descartes' most famous conclusion: cogito, ergo sum ("I think, therefore I am"). This statement becomes the foundation of Descartes' epistemology, as it establishes the self — or the thinking subject — as the first indubitable truth. For Descartes, the act of thinking is proof of existence, as doubting or thinking implies a thinking subject.

Spinoza, in his presentation of Descartes’ thought, underscores the significance of this conclusion. The cogito is the starting point for Cartesian metaphysics, where Descartes distinguishes between two fundamental substances: res cogitans (thinking substance or mind) and res extensa (extended substance or body). Descartes’ dualism asserts that the mind, characterized by thought, and the body, characterized by extension, are two distinct substances that interact but are fundamentally different in nature. The mind is indivisible, immaterial, and capable of reasoning, while the body is divisible, material, and governed by the laws of physics.

In the Principles of Cartesian Philosophy, Spinoza explains Descartes' arguments for the existence of God, which is central to his system. Descartes believes that the idea of an infinitely perfect being must have originated from such a being, as finite minds cannot conceive of infinite perfection on their own. Therefore, God exists as the cause of this idea. Furthermore, Descartes argues that God’s existence guarantees the reliability of clear and distinct perceptions — the foundation of certain knowledge. Since God is not a deceiver, humans can trust that their clear and distinct ideas correspond to reality. Thus, Descartes links the certainty of knowledge to the existence of a benevolent, non-deceptive God.

Spinoza presents Descartes’ theory of knowledge in which he distinguishes between different levels of cognition. The lowest level is sensory perception, which is often misleading and unreliable. The second level is imagination, based on sense experiences, which can form erroneous ideas. The highest form of knowledge is intellect or reason, which is the source of clear and distinct ideas. Descartes argues that only through reason can humans attain true knowledge, which is certain and immune to doubt.

In his critique and expansion of Descartes’ epistemology, Spinoza introduces his own emerging ideas. While Spinoza agrees with Descartes’ emphasis on reason as the path to true knowledge, he diverges in his treatment of the relationship between mind and body. For Descartes, the mind and body are two separate substances that interact in a causal relationship, though how this interaction occurs remains a point of ambiguity in Cartesian philosophy. Spinoza, however, does not accept this dualism. In his later work, Spinoza would propose a monistic system, arguing that mind and body are not distinct substances but rather two attributes of a single substance — God or Nature. Spinoza’s critique of Cartesian dualism is subtle in the Principles, but it becomes more explicit in his later writings.

The Principles of Cartesian Philosophy also engages with Descartes’ ideas on the physical universe. Descartes’ mechanistic view of the universe is one of his most significant contributions to modern philosophy. He argues that the material world operates like a machine, governed by mathematical laws. All physical phenomena, according to Descartes, can be explained in terms of motion, size, shape, and the interaction of particles. The universe, in this view, is deterministic, with no need for final causes or purpose (teleology) in explaining physical processes. Descartes rejects Aristotelian physics, which sought explanations in terms of purposes or ends, and instead offers a physics based purely on efficient causes.

Spinoza’s presentation of Cartesian physics highlights Descartes’ belief in the conservation of motion. Descartes posits that God, at the moment of creation, imparted a certain quantity of motion to the universe, and this quantity remains constant. The physical world, then, is a closed system in which the amount of motion is preserved, even though it may change forms. Descartes’ laws of motion, including the law of inertia, become foundational principles in the development of modern science.

However, Spinoza begins to distance himself from Descartes in his treatment of nature and the laws governing it. Descartes sees nature as a mechanistic system set in motion by God, whereas Spinoza would later develop a view in which nature is not merely a machine created by God but is identical with God. For Spinoza, God and Nature are one substance, and the laws of nature are expressions of God’s essence. This pantheistic interpretation of God and nature is absent in the Principles of Cartesian Philosophy, but Spinoza’s approach to Descartes’ physics anticipates this later development.

Another crucial aspect of Cartesian philosophy that Spinoza presents is the notion of free will. Descartes argues that human beings possess free will because the mind is not bound by the deterministic laws that govern the body. The mind has the ability to affirm or deny ideas, to choose between different courses of action, and to control the body’s movements. Descartes claims that free will is a gift from God, and it is a sign of the mind’s independence from the body. Yet, Descartes also acknowledges that the mind’s freedom is limited by ignorance, as people often make wrong choices due to a lack of knowledge.

In his exposition of Descartes’ views on free will, Spinoza does not offer an explicit critique, but in his later work, he radically departs from Descartes on this point. Spinoza famously denies the existence of free will in the traditional sense, arguing instead for a deterministic universe in which everything, including human thoughts and actions, is determined by prior causes. For Spinoza, the belief in free will is an illusion born from ignorance of the true causes of our actions. The human mind, like everything else in nature, operates according to the same laws of necessity that govern the physical world.