Descartes and Spinoza: Reason as Foundation

Cogito: Beginning Everything Anew

René Descartes (1596–1650) decided to start from a blank slate. Like an architect who discovers that the foundation of a house is rotten, he chose to demolish the entire building of knowledge and rebuild it—from a solid base. His method of doubt: can one doubt this? If yes—we discard it. Our senses deceive us. Mathematical truths? What if an evil demon arranges things so that 2+2 appears to us as 4, though in reality, it is not. What is left?

“I think, therefore I am” (Cogito ergo sum). If I doubt—I think. If I think—I exist. This cannot be disputed: doubting itself requires someone who doubts. This is the Archimedean point—the only firm support from which the entire structure of knowledge can be rebuilt.

Descartes is a dualist: the world consists of two substances. Res cogitans is the thinking substance, soul, mind. Res extensa is the extended substance, matter, body. They are fundamentally different: the soul is unextended and indivisible, the body is extended and divisible. How do they interact? Descartes did not find a convincing answer (the pineal gland is not an answer). This is the psychophysical problem that has haunted philosophy and science to this day.

Method and Science

Descartes was not only a philosopher but also a mathematician (analytic geometry, the Cartesian coordinate system) and physicist. His “Discourse on the Method” (1637) is a manifesto of a new approach to knowledge: break a problem into parts, begin with the simplest, proceed to the more complex, make complete lists. This is the method of reductionism, which became the foundation of experimental science.

Descartes dreamed of a unified tree of science: roots—metaphysics, trunk—physics, branches—medicine, mechanics, ethics. The science of the 17th–18th centuries realized this project—though on a different basis than Descartes imagined.

Spinoza: God or Nature

Baruch Spinoza (1632–1677) is the most radical rationalist. He wrote the “Ethics” in geometric order: axioms, theorems, proofs—just like Euclid. Rationalism is embodied in the very form of the book.

His ontology: only one substance exists—God, or Nature (Deus sive Natura). There are no two substances as in Descartes. Thought and extension are two attributes of the one substance. Concrete things are modes, finite manifestations of the infinite substance.

This is pantheism: God is not a separate creator from nature, but nature itself in its infinity. There is no providence, no miracles, no personal God. It is not surprising that Spinoza was excommunicated from the Amsterdam Jewish community at the age of 27—this is one of the most severe excommunications in Jewish history.

In ethics, Spinoza is also radical. Freedom is not freedom of will (which does not exist; everything is determined). Freedom is knowledge: a person is free when they understand the causes of their actions and act in accordance with their nature, and not from blind passions. The sage does not struggle against the nature of things—he understands it and lives in harmony with it.

Locke: The Origin of Knowledge from Experience

John Locke (1632–1704) is the opposite of rationalists. He is an empiricist: knowledge comes from experience, not from innate ideas. The mind of a child is a tabula rasa, a clean slate. Experience writes its content upon it. There is nothing in the mind that was not previously in the senses (with one caveat: “except the mind itself,” Leibniz will add).

Locke distinguishes primary qualities (extension, shape, motion—they are really in things) and secondary qualities (color, taste, smell—they are in us, not in things). This distinction turned out to be fundamental for physics: Newton built mechanics on primary qualities.

In politics, Locke is the father of liberalism. Two Treatises of Government (1689): the state arises from a social contract to protect natural rights—life, liberty, property. If the state violates these rights, the people have the right to change it. These ideas form the basis of the American Declaration of Independence.

Question for reflection: Descartes built knowledge on the self-evidence of thought; Locke—on experience. In your professional practice, what do you rely on more: on logical deductions from principles or on data from experience? When is one approach more reliable than the other?