Descartes doubted everything that could be doubted and found one certainty, "I think, therefore I am". From it he argued to God and the external world, and split reality into thinking and extended substance.
Central question
What can be known with certainty, as a foundation for the sciences?
Method
Descartes seeks a method that lets an ordinary mind reach certainty: doubt everything that can be doubted, find a first truth that survives the doubt, and go forward in order from what is simplest and best known. How René Descartes works ↓
Created reality consists of two kinds of substance, thinking things whose whole nature is thought and bodies whose whole nature is extension; both depend for their existence at every moment on God, the only substance in the strict sense.
Stated in the textres cogitans, res extensa, substantia, attributum principaleDraft — not yet reviewed
God as infinite substance (Principles I.51), on whom finite substances depend for their continued existence (AT VII 48–49), stands above the two kinds.
›UniversalsConceptualism
Universals are only modes of thinking: they arise when we use one idea to think of all the individuals that resemble one another, and exist nowhere but in the mind.
Stated in the textuniversalia, modi cogitandiDraft — not yet reviewed
God's existence can be proved by natural reason, at least as certainly as any truth of geometry: from the idea of an infinite being that I could not have caused, and from the idea of a supremely perfect being, which includes existence.
Stated in the textidea Dei, realitas objectiva, ens summe perfectumDraft — not yet reviewed
He also accepts revealed truths beyond reason (Principles I.25) but sets them aside as theology, so `faith-and-reason` would describe his faith rather than his philosophy. The Fifth Meditation claims at least the certainty of geometry (AT VII 65–66); the dedicatory letter (AT VII 1–6) claims more.
›Soul and bodySeparable soul
Because I clearly understand myself as a thinking, unextended thing and body as an extended, unthinking thing, God can make each exist without the other, so the mind is really distinct from the body; yet it is joined to it closely enough to make one whole, not lodged in it like a sailor in a ship.
Stated in the textdistinctio realis, res cogitans, unioDraft — not yet reviewed
The mind is a substance distinct from the body and is not destroyed by the body's corruption, which gives grounds for hope in an afterlife; he claims no more, since only God's power could annihilate it.
Scholarly consensusmens, immortalitas, substantia incorruptibilisDraft — not yet reviewed
The Meditations promised to prove the soul's immortality (AT VII 2–3), but the Synopsis concedes the full argument needs the whole of physics.
›The cosmosCreated from nothing, with time
There is no doubt the world was created at the start with all its perfection, as faith teaches; Descartes nonetheless explains it as if it had developed from a chaos by the laws of motion, without claiming that this is how it happened.
Stated in the textcreatio, hypothesis, leges naturaeDraft — not yet reviewed
›Freedom and determinismFree, not determined* (contested reading)
Free will is self-evident and the greatest perfection in us: we can give or withhold assent, and absolutely speaking we can even turn from a clearly known good to show our freedom, though morally speaking we scarcely can; how this fits divine preordination is beyond our grasp.
Another reading. Chappell ("Descartes's Compatibilism", 1994): freedom is spontaneity, the more clearly the intellect shows the true and the good the freer the assent, and indifference is the lowest grade of freedom (AT VII 57–58), a view compatible with determination by reasons.
Across the works. Kenny ("Descartes on the Will", 1972): the Fourth Meditation's freedom of spontaneity gives way to a two-way power only in the letter of 9 February 1645 (AT IV 173–175, probably to Mesland), so the libertarian view is a late development.
Contested readingFourth Meditation (1641) through the letters of 1644–45libertas, arbitrium, indifferentia, spontaneitasDraft — not yet reviewed
The coding follows Ragland, The Will to Reason (2016), who reads a consistent power of alternatives from 1641 on.
›CausationEfficient causes only · Real causes under a free first cause* (contested reading)
Physics should seek efficient causes, not God's purposes, which are hidden from us. God is the first and general cause of motion and conserves the world by continually creating it, and the laws of nature that follow from his constancy are secondary causes of particular motions. By the natural light there must be as much reality in the total cause as in its effect, and even the eternal truths are necessary only because God freely willed them.
Another reading. Garber (Descartes' Metaphysical Physics, 1992) reads him as holding that God alone causes motion in inanimate bodies, which is occasionalism for body on body.
Contested readingMeditations III–IV (1641); Principles I–II (1644); letters of 1630 and 1644causa efficiens, causa prima, causae secundae, leges naturae, creatio continua, lumen naturale, veritates aeternaeDraft — not yet reviewed
`secondary-causes` fits the laws as secondary causes and the dependence on God's free will, including for the eternal truths, but it is disputed whether bodies themselves act; minds do.
Epistemology
›Sources of knowledgeReason alone
Even bodies are known not by the senses or imagination but by the mind's inspection alone, as the wax shows; the senses give confused information useful for life, and knowledge rests on clear and distinct perceptions of the intellect.
Stated in the textsolius mentis inspectio, clare et distincte, intuitusDraft — not yet reviewed
Doubt stops at my own existence, which is true whenever I think of it, even if an all-powerful deceiver tries to mislead me; from there, a God who is no deceiver guarantees whatever I clearly and distinctly perceive.
Stated in the textcogito, certitudo, clare et distincte, Deus non fallaxDraft — not yet reviewed
The step "God guarantees" faces the Cartesian circle: Arnauld objects that clear and distinct perception is used to prove the God who guarantees it (Fourth Objections, AT VII 214; reply AT VII 245–246). Whether the cogito itself is an inference or a simple intuition is also disputed: he denies it is deduced by syllogism (AT VII 140), and Hintikka (1962) reads it as performative. Gassendi's objection that any action, such as walking, would prove existence as well is answered in the Fifth Replies (AT VII 352): only the awareness of walking, a thought, is certain.
›Innate knowledgeInnate knowledge
Some ideas, such as those of God, of the mind, of extension and of the eternal truths, are innate; they are present in the mind as a faculty or disposition, as some families are disposed to certain illnesses, and experience only occasions our thinking of them.
Stated in the textideae innatae, adventitiae, a me ipso factaeDraft — not yet reviewed
Because innateness is a disposition rather than present content, the view borders on `innate-structures`.
›TruthCorrespondence
Truth is the conformity of thought with its object, a notion too clear to define; a judgment errs when it takes an idea to resemble or conform to something outside the mind that it does not.
Stated in the textveritas, conformitasDraft — not yet reviewed
The eternal truths are themselves created by God's free will (to Mersenne, 15 April 1630, AT I 145), a further thesis no option records.
›Epistemic justificationEvidence of what is given
Whatever I perceive very clearly and distinctly is true, and I err only when the will affirms beyond what the intellect perceives in this way. A clear and distinct perception compels assent while I attend to it, but a conclusion I merely remember having demonstrated can be doubted until I know that a God who is no deceiver exists; so the certainty and truth of all knowledge depends on knowing God, and an atheist geometer has no true science. Firm conviction that nothing could shake is all we can ask for, even if it might seem false to an angel.
Another reading. Doney ("The Cartesian Circle", 1955) reads the divine guarantee as covering only remembered demonstrations, not present clear and distinct perceptions, which removes the circle.
Another reading. Frankfurt (Demons, Dreamers, and Madmen, 1970) reads the Meditations as showing that reason does not undermine itself, a justification by consistency rather than by correspondence with things.
Stated in the textMeditations (1641) with the Second Replies; Principles of Philosophy (1644)clare et distincte percipere, scientia, persuasio, regula generalisDraft — not yet reviewed
The divine guarantee is a second element the option does not show: present evidence suffices while attended to, but stable science needs the knowledge of God. Arnauld's objection that this argues in a circle is in the Fourth Objections (AT VII 214).
Axiology
›The highest goodFlourishing through virtue* (contested reading)
The supreme good is a firm and constant will to do what one judges best, which is virtue and the one thing fully in our power; the contentment that follows from it is happiness.
Another reading. Because the supreme good is the good use of free will and contentment follows from it, the view anticipates the structure of a good will crowned by happiness.
Contested readingsouverain bien, vertu, contentement, béatitudeDraft — not yet reviewed
An action is right when it comes from the resolution to follow what reason judges best, even where the judgment proves mistaken; generosity, the esteem of oneself as the free master of one's will, is the key to all virtues.
Scholarly consensusrésolution, générosité, morale par provisionDraft — not yet reviewed
›Virtue and knowledgeKnowledge plus habituation* (contested reading)
Virtue lies in the will's firm resolution, helped by knowledge of the good, and the passions can be retrained by habit so that even weak souls can master them.
Another reading. Judging well is enough for acting well (Discourse III, AT VI 28), and no one can sin while clearly seeing that an act is wrong (to Mesland, 2 May 1644, AT IV 117), so Descartes is an intellectualist about virtue.
Contested readingrésolution, habitude, passionsDraft — not yet reviewed
The intellectualist texts are Discourse III (AT VI 28) and the letter to Mesland of 2 May 1644 (AT IV 117); both are paraphrased here.
›The state and legitimacyNot addressed
Not addressed. Descartes offers no political theory and says that reforming states is not the business of private persons but of those God has set over peoples. His comments on Machiavelli's Prince in letters to Elisabeth (September 1646) concern a prince's conduct, not the best order.
Descartes leaves the order of the state to sovereigns and writes nothing on what the best order is.
›Beauty and artJudgment of taste* (contested reading)
Beauty and pleasantness are not in the object alone but a relation between our judgment and the object; since judgments differ, nothing has a fixed measure of beauty. Music pleases and moves the passions through proportions suited to the senses.
Another reading. The view answers what beauty is, not what art and beauty are worth, and it makes beauty vary with each person's judgment, claiming no general agreement; on this reading no option fits and Descartes has no account of their value.
Contested readingCompendium of Music (1618) and letter to Mersenne (1630)le beau, l'agréable, proportioDraft — not yet reviewed
`taste` fits loosely: Descartes makes beauty relative to the judge and grounds musical pleasure in proportion, without the option's claim to general agreement.
›JusticeNot addressed
Not addressed. Descartes gives no account of what justice is. His provisional morality keeps to the laws and customs of his country, and commenting on Machiavelli to Elisabeth he remarks only that justice between sovereigns has other limits than between private persons.
Descartes leaves justice to law and to those who govern, and writes no account of it.
God did not will things because he saw that they were good; they are good because he willed them, as all eternal truths depend on his free will as their efficient cause. For human beings, what to pursue is judged by reason, and beauty and pleasantness are relative to our judgment.
Stated in the textindifferentia, veritates aeternae, bonumDraft — not yet reviewed
The Sixth Replies speak of the goodness of what God creates, within the doctrine of created eternal truths; how far this reaches human moral value is not spelled out. # check: AT VII page for "good because he willed" (435–436).
* contested reading · open a row for the explanation and its sources
Method روش و شیوه اندیشهورزی فلسفی
Descartes seeks a method that lets an ordinary mind reach certainty: doubt everything that can be doubted, find a first truth that survives the doubt, and go forward in order from what is simplest and best known. He sets this out as a narrated method in the Discourse, carries it out as meditation in the Meditations, and gives it textbook form in the Principles.
Posing questions
Descartes begins from his own beliefs rather than from authorities, asking which of them could be false. Once in a lifetime, he says, one must demolish everything and begin again from the foundations, so that the question is first what can be known with certainty at all. Problems are then divided into as many parts as possible and taken in order, starting from the simplest. The questions he poses about God and the soul are framed as first philosophy, the roots of a tree whose trunk is physics and whose branches are medicine, mechanics and morals.
The Discourse gives four rules: accept only what is clearly and distinctly known, divide difficulties, proceed in order from simple to complex, and make complete enumerations. The doubt of the First Meditation is a procedure, not a conclusion: it uses dreams and a deceiving God to clear away all that is less than certain, until the thinker finds that he must exist while he thinks. In the Second Replies he distinguishes analysis, which shows the way a thing was found and which the Meditations follow, from synthesis, the geometrical order of definitions, axioms and propositions, of which he gives a sample.
He sets aside the learning of the schools not by refuting it point by point but by applying the doubt to it: what rests on probable reasoning and authority does not pass. The Meditations were published with objections from Hobbes, Arnauld, Gassendi and others and with his replies, so that criticism and answer appear together. Against the Jesuit Bourdin he defends the doubt with the image of a basket of apples, emptied so that the rotten ones can be thrown out before the sound are put back.
The intellect, by clear and distinct perception and by the natural light, is the source of certainty; whatever is clearly and distinctly perceived is true, once God is known not to deceive. The senses are given for the preservation of the body and teach what is useful rather than what bodies are, and the imagination serves mathematics but not knowledge of mind or God. Error arises when the will affirms beyond what the intellect perceives. In physics, experiments are needed to decide between the ways in which effects could follow from the principles.
The Discourse is written in French for anyone with good sense, as the story of one mind and its choices, offered as a fable to imitate or not. The Meditations are a sequence of six exercises in the first person that the reader is asked to perform, slowly and in order, not merely to read; the preface warns off readers unwilling to meditate seriously. The Principles recast the system in numbered articles fit for the schools. He also managed how his views reached readers: he told Mersenne that the Meditations contained the foundations of his physics but asked him not to say so.
méthode, dubitatio, clare et distincte percipere, lumen naturale, ordre des raisons, analysis, synthesis, ego cogito ergo sum
Arguments
›I think, therefore I amThat I am, that I exist, is necessarily true whenever I assert it or conceive it, and what I know myself to be is a thinking thing. Descartes adds that this is known by a simple intuition of the mind, not deduced by syllogism (AT VII 140); whether it is an inference at all is disputed (Hintikka, 1962, reads it as performative).
1Whatever admits the slightest doubt is to be set aside as if false, including the senses, the existence of bodies and the truths of mathematics, which an all-powerful deceiver might falsify.
2If I am persuaded of something, or doubt, or am deceived, then I am thinking.
3A deceiver, however powerful, can never bring it about that I am nothing so long as I think that I am something.
∴That I am, that I exist, is necessarily true whenever I assert it or conceive it, and what I know myself to be is a thinking thing. Descartes adds that this is known by a simple intuition of the mind, not deduced by syllogism (AT VII 140); whether it is an inference at all is disputed (Hintikka, 1962, reads it as performative).
David Hume objects. (Applied; Hume does not name Descartes.) Introspection finds only particular perceptions and never a self that has them; the "I" is a bundle of perceptions, so the cogito gives no knowledge of a thinking substance.
Immanuel Kant objects. The "I think" must be able to accompany all my representations, but it is only the formal unity of consciousness; inferring from it that I am a simple, persisting substance is a paralogism.
›The trademark argument for God's existenceGod, who has formally all the perfections my idea represents, exists, and placed the idea in me as a craftsman's mark on his work.
1I have an idea of God, a substance infinite, independent, supremely intelligent and powerful.
2There must be at least as much reality in the total efficient cause of an idea as there is objective reality in the idea.
3I am finite, and doubt and desire show that I lack perfections, so I cannot be the cause of an idea with infinite objective reality.
4The idea of the infinite is not derived from the finite by negation, since my grasp of my own limits presupposes it.
∴God, who has formally all the perfections my idea represents, exists, and placed the idea in me as a craftsman's mark on his work.
David Hume objects. (Applied; Hume does not discuss Descartes here.) The idea of God is formed from experience: we reflect on the operations of our own minds and augment their goodness and wisdom without limit, so it needs no infinite cause. Descartes anticipates this: a merely potential increase of my perfections cannot account for an idea of the actually infinite (AT VII 46–47).
I think · therefore I amThe one thing that survives the most radical doubt: while I think, I cannot fail to exist. The Meditations puts it as "I am, I exist", true whenever I think it.2 links to other thinkers →
thinking thing · extended thingMind and body are two substances, each with its own principal attribute, thought and extension. Because each can be clearly understood without the other, God can make them exist apart.2 links to other thinkers →
to perceive clearly and distinctlyA perception is clear when it is present and open to the attentive mind, and distinct when it is so sharply set apart from all others that it holds only what is clear. What is so perceived is true, since God is no deceiver.
innate ideasSome ideas seem innate, some adventitious (from outside), some made up by me. Innate ideas, such as those of God, mind and mathematical essences, come from the mind's own power of thinking, not from the senses.
methodical doubtOnce in life, withhold assent from everything that can be doubted at all (the senses, mathematics, the world) by supposing a deceiving evil genius. What survives can found the sciences.1 link to other thinkers →
objective reality (of an idea)The reality an idea has through what it represents, as against its reality as a mode of thought. Since a cause must have at least as much reality as its effect, the idea of an infinite God must come from God.
generosity · nobility of soulThe crowning virtue of the Passions: knowing that nothing is truly one's own but the free use of one's will, with a firm resolve to use it well. Descartes calls it the key to all the other virtues.
Thinkers named, not addressed, in the texts Hekmat holds. Naming someone is not evidence of influence.
Names in their works
None in the texts held here.
Named by
›Friedrich Nietzsche6 passages · 5 works
The Antichrist 14… this as it may, he is certainly the most interesting! As regards animals, Descartes was the first, with really admirable daring, to venture the thought that …
Beyond Good and Evil 54… What does all modern philosophy mainly do? Since Descartes—and indeed more in defiance of him than on the basis of his procedure—an attentat has been made on …
The Birth of Tragedy 12… and remove every doubt as to the reality of the myth: as in the case of Descartes, who could only prove the reality of the empiric world by an appeal to the …
