Dr. Ari Santas’ Notes on

Introduction to Rene Descartes


A. Biography (1596-1650)


-Descartes was born in 1596 in La Haye, France


-his health was frail early in life; luckily, he had parents with enough money and sympathy to let him just lie around in bed in the mornings


-this began an important habit of daily reflection and meditation


-early education was at La Fleche, a small Jesuit college where he received training in the Scholastic--Aristotelian--tradition


-later he studied law at the University of Poitiers


-generally, it is said that Descartes admired his teachers but rejected most of what they taught him


-with one notable exception--mathematics


-in 1618 he joined the army and did a lot of traveling abroad (minus combat)


-in Nov. 1619 (still in the army), while meditating on the uncertainty of his knowledge and on the certainty of Mathematics, Descartes had a flash of insight

-it revealed to him how certainty is to be gained in the sciences

-that night he had a series of dreams that he interpreted as a divine sign that he was on the right track


-during the 1620's he, being frustrated with initial attempts to work out the details of his new science, decided to live it up for a while (gambling, etc.)


-around 1629, at the advice of some friends, he went to the Dutch Republic and began a serious attempt to set his ideas to paper

-1634 Le Monde--suppressed because of Galileo's condemnation (he burned it)

-1637 Discourse on Method

-1641 Meditations on First Philosophy

-1644 Principles of Philosophy


-in 1649, the young Queen Christina of Sweden asks Descartes to come to Stockholm and instruct her in philosophy and mathematics (some say something else too)

-reluctantly, and against the advice of friends, he accepts the offer


-due to her rigorous schedule (which included appointments before dawn) and to his frail health (and some say to something else) in the year 1650 he contracted pneumonia and died


B. The Dream


-Descartes had been very dissatisfied with the state of scientific knowledge in his time


-like a house built haphazardly on an unstable foundation, science was a patchwork of theory and observation, a little here, a little there, with no order or a sense of reliability


-Descartes felt that the time had come to raze the house and start again


-but what materials to use? and in what order?


-in contrast to physical science, mathematics was a highly developed discipline which proceeded step by step, losing no certainty in moving from one idea to the next


-Descartes' dream was to find a way to combine the certainty of mathematics with the study of physical reality


-for him, probability in the sciences is not enough


-making his discovery would clear the ground for his reconstruction


-the answer to his prayers was a realization that if one could find a means of representing the motions of bodies mathematically, then one could derive results about matter with the same kind of certainty that one could find in pure math


-such a realization amounted to this (something Galileo apparently said):


-the book of nature is written in the language of mathematics


-one of his tasks, then, was to show how matter could be represented mathematically


-to do this he invented analytic geometry


-it was his belief (and dream) that eventually everything in the world could be known mathematically, and not only that:


-that every event, past, present, or future could be demonstrated a priori, right down to today's weather report


C. Metaphysical Point of View


-Descartes' means of combining math and physics and of separating the physical sciences from uncertainty and disarray was to posit a metaphysics of dualism


-there are two distinctly different types of substances: mental, thinking substances and physical, non-thinking substances


-mind, or, mental substance, is indivisible, unextended, and immortal



-body, or, physical substance is divisible, extended, and changeable



-such a conception was useful for two kinds of reasons:


-first, it allowed Descartes to assuage the Church at least with respect to morals


-there is no need to experiment and question the moral maxims offered by traditional Christianity


-science could divorce itself from moral and value oriented questions


-second, Descartes could now remove final causes--a source of great specious speculation in science--from the cosmic picture and look at the world mechanically


-once we can describe the world as a mechanism, we can then define objects and their motions mathematically and crank out results with the same rigor as the theoretical math of the Greeks



-one should note, however, that there is a third element in Descartes’ universe: God


-technically, then, Descartes’ universe is not a dualism but a triadism


-though later on many will drop the God hypothesis and will be left with a dualism


-God will be invoked throughout Descartes’ metaphysics when the going gets tough (somewhat reminiscent of St. Augustine's Confessions)


D. Epistemological Point of View


-along with a Dualism in metaphysics came a dualism in epistemology


-our interaction with the world takes place either through the senses, or through the intellect



-for Descartes, the senses are part of our bodies and are therefore disjoined from the mind



-the intellect, on the other hand, comprises the essence of mind



-it is Descartes' belief that the senses are unreliable means of understanding nature, and knowledge can only come from the workings of Reason


-it is Reason, not the senses, that defines objects mathematically and deduces logically their properties


-the senses report either illusions or mere secondary (i.e., accidental) properties of things



-Descartes' epistemology, accordingly, is called rationalistic rather than empiricistic


-Rationalism vs. Empiricism



-the method of procedure in the study of nature, then, is to define mathematically the substances at hand and derive from one's axioms the results (i.e., theorems)


-the axioms will be those found in mathematics as well as those derived from the metaphysics


-the rules of inference are the guiding principles of rationality


E. The Guiding Principles of Rationalism


-inferences in this system are to be drawn by appeal to the traditional principles of rationality



-The Principle of Contradiction and


-The Principle of Sufficient Reason



-The Principle of Contradiction (also Non-Contradiction, sometimes called the Principle of Identity) has it's roots in Ancient Greece and has been used extensively in math as well as the Scholastic philosophy of the Middle Ages (Anselm, for instance)


-basically, it states that:


(a) what implies contradiction is necessarily false;


(b) what opposes contradiction is necessarily true


-it is the basis of all reductio ad absurdum arguments



-The Principle of Sufficient Reason also has its roots in Ancient Greece (remember Anaximander?) and is related to the celebrated Principle of Causality as well as the medieval dictum: "ex nihilo nihil fit" (out of nothing comes nothing, or, “nothing comes from nothing”)


-basically, it states that:


-everything has a (good) reason for being the way it is and not otherwise


-this principle is used in various forms throughout the modern period



-the two principles are often combined in a single demonstration and even conflated



-by the time Immanuel Kant (1724-1804) writes his Critiques, both these principles have undergone important changes either in content or in domain of application