Renaissance/Early Modern
René Descartes
1596–1650
“Archimedes, in order that he might draw the terrestrial globe out of its place, and transport it elsewhere, demanded only that one point should be fixed and immovable; in the same way I shall have the right to conceive high hopes if I am happy enough to discover one thing only which is certain and indubitable.”
René Descartes was a French mathematician and philosopher who sought a method secure enough to rebuild knowledge after systematic doubt. In the and the he finds one indubitable point: he exists as a thinking thing. From that certainty he argues for God and recovers the external world, distinguishing thinking substance from extended substance. Mind and body become really distinct. Modern philosophy inherits both his demand for certainty and the mind-body problem his dualism leaves behind.
In the Conversation
41 of the Great Ideas
Theology & Metaphysics
God
God's existence is known by the intellect: the idea of a perfect being implies that being.
Soul
The soul is a thinking substance, essentially distinct from the body. 'I think, therefore I am.'
Being
I think, therefore I am: the first certainty is the being of the thinking self.
Cause
There must be at least as much reality in the cause as in the effect, and this leads the mind to God.
Immortality
The soul is a thinking substance entirely distinct from the body; its simplicity means it cannot be destroyed by natural causes.
Theology
God's existence can be demonstrated with mathematical certainty from the idea of a supremely perfect being.
Metaphysics
Metaphysics must be refounded on the certainty of the thinking subject; the Cogito replaces being as the first principle of philosophy.
Metaphysics
Change
Motion is simply the transfer of a body from one place to another; no potency, no act, no mystery.
Form
Substantial forms are obscure relics to be banished; nature is exhaustively explained by matter in motion and the geometry of extension.
Matter
Matter is extension, res extensa, a single geometrical substance whose whole essence is to occupy space.
Space
Extension is the essence of body; space and matter are identical, and there can be no vacuum.
World
The world is an extended substance governed by mechanical laws; God set it in motion, but all natural phenomena follow from matter and motion alone.
Quality
Extension, figure, and motion belong to bodies as they are; color, sound, and warmth exist only in the perceiving mind.
Quantity
Extension is the essence of matter: all physical properties reduce to geometrical ones, and the material world is nothing but quantity made actual.
Epistemology
Truth
Truth is what the mind perceives clearly and distinctly, certified by a non-deceiving God.
Knowledge
Knowledge must be built on clear and distinct ideas, beginning from the one thing that cannot be doubted.
Mind
Mind is thinking substance: distinct from body, and the first thing known.
Experience
The senses deceive; only clear and distinct ideas of the intellect are reliable, and some ideas are innate.
Will
The will is infinite in scope, and error arises when we affirm beyond what we clearly perceive.
Opinion
To escape opinion, suspend judgment about everything not clear and distinct; the thinking self, perceiving its own existence, gives us one piece of certain knowledge from which to rebuild.
Idea
Ideas are the mind's own contents; some are innate, placed in us by God, and known more clearly than any sensible thing.
Judgment
Error arises because the will outruns the understanding, affirming what the intellect does not clearly perceive.
Sense
The senses frequently deceive us; the mind alone, through clear and distinct ideas, reaches certainty.
Hypothesis
Doubt is the supreme hypothesis: assume everything false, and whatever survives that assumption becomes the foundation of knowledge.
Mathematics
Mathematics is the model for all knowledge, grounded in clear and distinct ideas and deductive chains of reasoning.
Logic & Method
Dialectic
Scholastic dialectic trains the tongue rather than the mind; clear intuition and orderly deduction must replace disputation as the instrument of discovery.
Principle
The first principle of knowledge is the Cogito: 'I think, therefore I am,' the one certainty that survives universal doubt.
Reasoning
Sound reasoning proceeds by chains of clear and distinct intuitions; each step must be as certain as the first principle.
Logic
True method is not the syllogism but a chain of intuitions and deductions proceeding by ordered steps from what is simple to what was obscure.
Induction
Against both Aristotelian demonstration and Baconian induction, genuine method requires intuition of simple natures and deduction: reason, not accumulated experience, is the source of certainty.
Science
True science is the universal mathematics — a single method of clear deduction from first principles that can explain all natural phenomena through the laws of matter and motion.
Philosophy & Practical
Nature
Nature is extended matter, knowable by mathematics. Mind alone is outside the mechanical world.
Wisdom
Wisdom requires a method of radical doubt that clears all uncertain foundations and rebuilds knowledge from certainty.
Philosophy
Philosophy must be rebuilt from the ground up on the indubitable foundation of the thinking self.
Man
Man is essentially a thinking thing; the mind is entirely distinct from the body, which operates as a machine.
Life & Nature
Life and Death
The body is a machine; life is a mechanical process, and only the rational soul distinguishes man from automata.
Animal
Animals are machines: complex automata without thought or feeling, moved entirely by the arrangement of their parts.
Element
Matter is extension alone, and the three elements differ only in the size and motion of their parts.
Medicine
The body is a machine, and medicine is the mechanics of living matter; complete knowledge of physics would give us mastery over disease.