René Descartes

Against skepticism, Descartes turns doubt against itself: he drives it to the point of hyperbole, supposing an evil genius who deceives him about everything, to see whether anything withstands it. Yet the very act of doubting presupposes a subject who doubts: I can call everything into doubt except that I am thinking, and therefore that I am. The cogito is no dogma laid down in advance but a certainty won through doubt itself, an indubitable foothold from which the whole of knowledge can be rebuilt. The conclusion is thus firmly dogmatic: full certainty is attainable, and skepticism refutes itself when pushed to its limit.

I think, therefore I am.Discourse on Method, IV

Meditations on First Philosophy, I and II · Discourse on Method, IV

Since the senses deceive us and yield only confused qualities, they cannot ground a certain science: only the understanding, which conceives geometrical extension clearly beneath the sensory appearances (the analysis of the piece of wax), reaches the nature of things. Descartes infers that the founding concepts, the idea of God, of extension, the mathematical truths, cannot come from experience: they are innate ideas placed in the understanding. All science then reduces to the intuition of simple natures and the deduction that links them, on the model of mathematics, which sharply separates him from the coming empiricism, for which nothing is in the mind that was not first in the senses.

Meditations on First Philosophy, III and V · Rules for the Direction of the Mind, III

Clear and distinct ideas reach the real as it is: guaranteed by the veracity of a non-deceiving God, they are not constructions of the mind but the true apprehension of the nature of things, such as the geometrical extension of the material world. This is a strong, metaphysically grounded scientific realism.

Meditations on First Philosophy, V and VI · Principles of Philosophy, I, art. 45 and II, art. 4

The project of the Meditations on First Philosophy is expressly foundationalist: to tear down every doubtful opinion and rebuild knowledge on a single unshakeable first principle, the cogito, whose certainty then supports the whole edifice. Knowledge rests on indubitable foundations, not on the mere coherence of a web of beliefs.

Meditations on First Philosophy, I-II

Knowledge is for him no speculative luxury: he wants to distinguish the true from the false in order to see clearly into his own actions and conduct his life with confidence. The method aims at shedding prejudice and hasty judgment, because a well-conducted life is regulated by established truths rather than received opinions.

I always had an intense desire to learn to distinguish the true from the false, in order to see clearly into my own actions and to walk with confidence in this life.Discourse on the Method, I

Discourse on the Method, I (1637)

Descartes makes the will the infinite faculty of the soul, that in which we most resemble God: it is the will, not the limited understanding, that can affirm or deny anything. This freedom of free will is the most immediate experience we have of ourselves.

Meditations on First Philosophy, IV · The Passions of the Soul, arts. 41 and 152

The self is a substance, a thinking thing, whose existence is grasped immediately in the cogito and whose identity depends on neither body nor memory. This is a substantialism of the subject, which also secures the soul's immortality.

Meditations on First Philosophy, II · Discourse on Method, IV

The whole Cartesian procedure is a withdrawal inward: it is by turning away from the senses and the world, in the solitude of meditation, that the mind grasps itself as a thing that thinks. The cogito is won through methodic introspection, the reflective examination of one's own thoughts becoming the ground of all certainty.

Meditations on First Philosophy, I and II · Discourse on Method, IV

The true self is the thinking thing; the body is a machine, distinct from the soul, to which the soul is joined. Descartes nonetheless acknowledges a substantial union of soul and body and rejects the image of the pilot in his ship, which tempers the pure instrumentalism somewhat.

Meditations on First Philosophy, VI; Letters to Elisabeth

Close in this to the Stoics, Descartes holds that adversity is the occasion to test one's own strength: generosity, the firm resolve to use one's free will well, yields an inner contentment that nothing external can remove, and that arises precisely from the effort to do well despite the ordeal. Suffering, mastered by judgment, thus becomes matter for a legitimate self-satisfaction, not a pure evil.

The Passions of the Soul, arts. 147-148 and 190 · Letters to Princess Elisabeth

Cartesian dualism really separates the soul, a thinking substance, from the body, an extended substance: nothing in the nature of the mind depends on the body, whose death therefore cannot reach it. Descartes presents it as an explicit aim of the Meditations to demonstrate, against the libertines, the immortality of the soul. Death is but the breakdown of a machine, the soul surviving it.

Meditations on First Philosophy, Dedicatory Letter and VI

Descartes holds the passions to be useful when well governed: the point is neither to suppress nor to follow them, but to make the soul their master through judgment and a firm will. Stoic in inspiration, his provisional morality bounds the will to what depends on us and counsels changing one's desires rather than the order of the world. Yet he joins to this the affirmation of a desire guided by reason: virtue lies in resolutely doing what one judges best, the source of an inner contentment even in failure. Detachment, sorting and affirmation balance out in him.

To strive always to master myself rather than fortune, and to change my desires rather than the order of the world.Discourse on Method, III

Discourse on Method, III · The Passions of the Soul, arts. 144-148 and 211-212

Deprived of thought and therefore of soul, animals are for Descartes mere automata, the famous beast-machine: they neither feel nor suffer in the proper sense, their cries being only mechanical effects. Moral consideration is thereby restricted to thinking beings alone, a strict anthropocentrism.

Discourse on Method, V · Letter to the Marquess of Newcastle, 23 November 1646

Reality divides into two irreducible substances: the thinking thing (res cogitans), whose essence is thought, and the extended thing (res extensa), whose essence is geometrical extension. This is Cartesian dualism, which grounds the possibility of an entirely material physics and an immaterial soul.

Meditations on First Philosophy, VI · Principles of Philosophy, I, arts. 51-54

Material nature is fully explained by the laws of motion and the shape of parts: the bodies of living beings, and animals themselves, are machines, devoid of soul. Descartes banishes the search for final causes from physics, reserving them to God, hence a residual share of theological finalism.

Discourse on Method, V · Principles of Philosophy, I, art. 28 and II

The cogito at first secures only my own existence: so long as an evil genius could deceive me even in my self-evident truths, doubt is not defeated. Proving God therefore becomes the keystone of the system. Descartes offers two proofs: the idea of infinity within me, which cannot arise from a finite being, demands an infinite cause (Meditation III); and existence belongs to the essence of the perfect being as the equality of its angles belongs to the triangle, the ontological proof (Meditation V). Now a perfect God cannot be a deceiver, deception betraying a defect: his veracity therefore guarantees that what I conceive clearly and distinctly is true. Far from inherited theism, the position is the keystone that lifts doubt and grounds the whole of science.

Meditations on First Philosophy, III and V · Discourse on Method, IV

Once material nature is nothing but extension governed by the laws of motion, knowing the forces of bodies as one knows a mechanism allows them to be applied to every use, medicine first of all. Descartes replaces the speculative philosophy of the Schools, which contemplates essences, with a practical philosophy that transforms: the end of knowledge is no longer to understand a given order but to harness it. Nature ceases to be a community or a mother and becomes a domain to be possessed, a programme that inaugurates the modern technological relation to the world.

Instead of that speculative philosophy taught in the schools, we may find a practical one […] and thus render ourselves, as it were, masters and possessors of nature.Discourse on Method, VI

Discourse on Method, VI

In The Passions of the Soul, the passions are motions of the soul caused by the body's spirits: they are neither to be suppressed nor blindly followed, but governed by reason and a firm will. Mastery lies in an enlightened use of judgment, which leans toward intellectualism without denying the worth of well-ordered passions.

The Passions of the Soul, arts. 27-50 and 211-212

The living body, the human body included, is fully explained as a machine: circulation, digestion, and the motion of the limbs reduce to the sole laws of shape and motion, with no superadded vital principle required. Life is reduced to mechanism, the soul belonging to another order entirely.

Discourse on Method, V · Treatise on Man

Dedicating his Meditations to the Sorbonne, Descartes argues that the existence of God and the immortality of the soul, truths of faith, can be demonstrated by natural reason. Faith and reason thus agree: far from contradicting each other, philosophy comes to confirm and rationally ground the teachings of religion.

Meditations on First Philosophy, Dedicatory Letter to the Sorbonne · Discourse on Method, IV

The argument rests on a principle: what I clearly and distinctly conceive as able to exist apart really exists apart, since God could create it so. Now I can conceive my mind, pure thinking thing (res cogitans), with nothing corporeal attributed to it, and body, pure extension (res extensa), with no thought. My essence is therefore to think, and the mind is really distinct from the body, a substance of another nature than the brain. This substance dualism breaks with the Aristotelian soul, form of a body, and at one stroke frees matter for a purely mechanistic physics; yet it bequeaths the problem, which Descartes will struggle to solve, of their union and interaction.

Meditations on First Philosophy, VI