Descartes

René Descartes (1596–1650) is the father of modern philosophy and the originator of the dominant framework of early modern thought. His method of systematic doubt and his formulation of the mind-body problem define much of Western philosophy from the 17th century onward.

Life

Born in La Haye, France (now renamed Descartes in his honor), he was educated by Jesuits, then pursued law before turning to mathematics and philosophy. He served briefly as a soldier, then spent most of his adult life in Holland, prizing isolation and quiet for sustained reflection. He died in Stockholm after accepting an invitation from Queen Christina of Sweden to teach her philosophy at five in the morning — reportedly dying of pneumonia from the cold.

Method of Radical Doubt

In the Meditations on First Philosophy (1641), Descartes undertakes a systematic program of Epistemology:

"I will withhold my assent from whatever is not completely certain and indubitable."

He identifies three grounds for doubt:

Illusions of the senses — perception sometimes deceives
The dream argument — I cannot distinguish dreaming from waking
The evil demon (malin génie) — an all-powerful deceiver might cause me to be wrong about everything, including mathematics

Cogito Ergo Sum

One thing survives radical doubt: the very act of doubting proves that something is thinking. Even if an evil demon deceives me about everything else, I must exist in order to be deceived:

Cogito, ergo sum — "I think, therefore I am."

This is the Archimedean point from which Descartes rebuilds knowledge. It established the thinking subject as the foundation of philosophy — a move that shapes all subsequent work, including Kant's and Hegel's.

Mind-Body Dualism

Descartes argued for substance dualism:

Res cogitans — thinking substance; the mind; non-spatial
Res extensa — extended substance; matter; spatial

This raises the interaction problem: how do two fundamentally different substances causally affect each other? Descartes answered (unconvincingly) through the pineal gland. This problem haunts Metaphysics and philosophy of mind to this day — see Consciousness.

God and Rationalism

In the Meditations, Descartes offers two arguments for God's existence:

Ontological argument — the idea of a perfect being must include existence (otherwise lacking something)
Causal argument — only an infinite being could cause the idea of infinity in my finite mind

He uses God's non-deceptiveness to guarantee that clear and distinct perceptions correspond to reality — bridging the gap opened by the evil demon doubt.

Mathematics and Method

Descartes was also a great mathematician — inventor of coordinate geometry (Cartesian coordinates). He believed mathematical certainty was the model for all genuine knowledge: proceed from clear, distinct, certain axioms by rigorous deduction.

Influence

Descartes established Epistemology — specifically the search for certain foundations — as the central task of modern philosophy
His substance dualism framed the mind-body problem that dominates philosophy of mind today (Consciousness)
Hume attacked Cartesian rationalism empirically
Kant absorbed and transformed Descartes' project
Phenomenology (Husserl) is partly a radicalization of Descartes' subjective turn

Epistemology — Descartes' method of doubt as a defining moment
Metaphysics — substance dualism and the nature of mind and matter
Consciousness — the mind-body problem originates with Descartes
Kant — the rationalist tradition Kant reformed
Hume — empiricist challenge to Cartesian rationalism
Free Will — the question of how the mind, as non-physical, can cause action
Phenomenology — continuing the first-person investigation of the knowing subject