Descartes and the Foundations of Modern Subjectivity (cogito, ideae adventitiae, res cogitans/extensa, mathesis universalis)
Fifth Lecture
by
Tanmoy Bhattacharyya
With René Descartes (1596–1650) the entire axis of Western philosophy tilts ninety degrees. The ancient and medieval question “Quid est ens qua ens?” is replaced by a new, apparently modest, but in reality explosive interrogative: “Quid mihi certum est?” What is certain to me? The hypokeimenon is no longer the οὐσία or the suppositum; it is now the ego cogitans. The real is no longer that which subsists per se but that which is indubitably clear and distinct to the res cogitans. This is the most radical inversion since Parmenides.
This lecture is a full-scale, technically merciless descent into the Cartesian system: the methodus and the regulae, the three substantiae (infinitum, cogitans, extensa), the mathesis universalis, ideae factae/innatae/adventitiae, the three grades of sensus, the ontological argument, the circulus cartesianus, the pineal gland and the animal-machine, the provisory morality, and the esoteric doctrine of the creatio aeterna of eternal truths. Every rare and exact term is used in strict seventeenth-century Latin: res cogitans/extensa, idea materialiter/formaliter/objective, clara et distincta perceptio, vis cogitandi, enumeratio, intellectio infinita, volitio indefinita, unio substantialis, passiones animae, inclinatio naturalis, error as privatio, etc.
1. The Methodic Doubt and the First Certainty
Meditations I–II stage the most devastating skeptical performance in history:
- All sensory knowledge is dubitable (dream argument)
- Even mathematics is dubitable (malus genius)
- The only indubitable remainder is the actus cogitandi itself: cogito, ergo sum is not a syllogism but the first primitiva notitia, an immediate intellectio of the ego as res cogitans.
The ego (εγώ) is defined negatively first: non spatium, non corpus, non imaginatio, non sensus; only pura vis cogitandi (pure thinking power).
2. The Three Grades of Idea and the Causal Principle
Meditations III introduces the most intricate taxonomy of ideas ever devised:
- Ideae innatae: truths of reason (e.g., “ex nihilo nihil fit”)
- Ideae adventitiae: apparently from senses
- Ideae a me ipso factae: fictions
Every idea, considered formally (as psychological act), has a causa. Considered objective (as representing), it contains a certain gradus realitatis. The pivotal axiom: “Nulla res ex nihilo fit” extends to ideas: there must be at least as much realitas in the causa as in the effect. Hence, the idea of God (ens infinitum, aeternum, immutabile, omnisciens, omnipotens, creator) cannot be produced by the finite ego and must have God Himself as causa.
3. The Two Proofs of God in Meditationes III and V
- Third Meditation: causal proof (a posteriori)
- Fifth Meditation: ontological argument redivivus “Existentia a Deo tam inseparabilis est ac a triangulo summa angulorum trium aequalis duobus rectis.”
Crucial Cartesian refinement: God is not ens summum (Aquinas) but ens infinitum, and His existence is known per ipsam ejus essentiam, not via causal inference alone.
4. The Circulus Cartesius and the Escape
Kant and Arnauld accused Descartes of vicious circularity: we need God to guarantee clear and distinct ideas, but we use clear and distinct ideas to prove God. Descartes’ reply (Responsiones IV) is subtle: the circle is only apparent because the atheist mathematician can have scientia of particular truths while denying God, but he cannot have scientia absoluta of the whole system without God as guarantor of memoria and continuata existentia of the ego.
5. The Dualism of Substantiae: Res Cogitans and Res Extensa
Principia Philosophiae II articulates the great scission:
- Res cogitans: inextensa, indivisibilis, libera
- Res extensa: mensura, figura, motus localis
- Res infinita: Deus
Attributes are principal and essential: thought is the attributum of res cogitans; extension of res extensa. Modes (e.g., volitio, imaginatio, sensus) are modifications of the attribute.
6. Mathesis Universalis and the Dream of a Single Science
Regulae ad Directionem Ingenii (written 1628, published 1701) contains Descartes’ most ambitious project: all sciences form una scientia, reducible to ordo et mensura. The famous “intuitus et deductio” method:
- Intuitus mentis: direct, non-temporal grasp of simple natures
- Enumeratio sive inductio: sufficient and ordered enumeration
- Reduction of the complex to the simple via analysis
The entire cosmos is to become a single deductive system more geometrico.
7. The Unio Substantialis and the Passions of the Soul
Despite radical dualism, Descartes must account for the evident interaction of mind and body. His solution:
- Unio substantialis: not a third substance but a modus mixtus produced by divine power
- Conarium (pineal gland): the single point where soul and body meet
- Passiones animae: thoughts caused by animal spirits, not by objects themselves
Les Passions de l’Âme (1649) classifies six primitive passions: admiration, amour, haine, désir, joie, tristesse. All others are species of these.
8. The Animal-Machine and the Denial of Bestial Souls
Traité de l’Homme and Description du corps humain reduce animals to automata strata ex machina. They lack res cogitans; their apparent purposefulness is purely mechanistic. This doctrine shocked contemporaries and opened the vivisection era.
9. The Provisory Morality and the Four Maxims
While awaiting the tree of philosophy to bear fruit, Descartes adopts a morale par provision:
- Obey laws and customs
- Be firm and resolute in action
- Master oneself rather than fortune
- Choose the best occupation (philosophy)
10. The Esoteric Doctrine: Creatio Aeterna of Eternal Truths
In letters to Mersenne (1630) and Mesland (1644), Descartes drops the bombshell: eternal truths (mathematical, logical, metaphysical) are freely created by God’s voluntas indefinita. 2 + 2 = 4 is true only because God decreed it so ab aeterno, and He could have decreed contradictions true by the same potentia absoluta. This is the most radical voluntarism in the history of philosophy and destroys the Greek principle of non-contradiction as necessary.
Key Technical Vocabulary (strict Cartesian Latin)
- res cogitans / extensa / infinita
- idea materialiter / formaliter / objective
- clara et distincta perceptio
- vis cogitandi
- intellectio / volitio
- intuitus mentis
- enumeratio sufficiens
- attributum principale
- modi affectiones
- unio substantialis
- conarium
- passiones animae
- animalia machinae
- morale par provision
- veritates aeternae creatae
- voluntas indefinita
- potentia Dei absoluta
- circulus cartesianus
- ego sum, ego existo
- scientia absoluta vs particularis
Study Questions (extremely advanced)
- Explain why the cogito is not a syllogism and why “ego sum res cogitans” is a notitia primitiva rather than a conclusion.
- Reconstruct the argument that the idea of God contains plus realitatis objectivae than the finite ego can produce. Why does Descartes insist this is not a scholastic argument?
- How does Descartes escape the circulus cartesianus in the Responsiones IV?obeli? Is the escape successful?
- Why does Descartes locate the unio substantialis in the pineal gland and nowhere else? What physical and metaphysical constraints force this choice?
- Using only the 1630 letters to Mersenne, show how the doctrine of created eternal truths annihilates the Greek and medieval concept of necessary being.
In our sixth lecture, we will enter the critical philosophy of Immanuel Kant: the Copernican revolution, phenomena vs noumena, the transcendental aesthetic and analytic, the antinomies, the paralogisms, the ideality of space and time, and the utter demolition of speculative metaphysics.
