RENÉ DESCARTES (1596-1650)


René Descartes was born in La Haye in Touraine as a son of an Aristocrat in the area,
studied at the Jesuit school at La Flèche and then lived in Paris.
Descartes joined in the army, stationed in Holland (1618-1619).
He further joined in Bavarian army (1619-1621) and experienced the 30 year war (1618-1648). Being an officer in the army (because he was an aristocrat), he did not want get up early in the morning but stayed in bed long, pondering on philosophical questions.
Descartes discovered the principle of science in the winter camp.
He lived in Paris for 4 years.
Descartes moved to Holland when he was 34 years of age and died there at the age of 54 years in 1649. those twenty years were the most philosophically productive years.

Descartes adopted Ovidius’ principle of “bene vixit, bene qui latuit.” (The one who hides well lives well.) In order to put this into practice, he moved his residence even 13 times.
Descartes did not live a life of ascetic: For a few years after 1634, there was a record that Descartes lived with Hélène.
Descartes got acquainted with Pfalzgrafen Elizabeth in 1643.
In an ardent request of Queen Christina, Descartes moved to Stockholm in 1649. She was very demanding and often dragged him out of his bed early in the morning, which was supposed to cause Descartes to have pneumonia and he died. If you visit the Museum of Natural History in Paris, you are able to see Descartes’ skull is exhibited in the same room as Pascal and Arnold.


1. Regulae ad directionem in genii (Regulations for directing the spirit)
presenting the thought of “mathesis universalis.”
axiomatization of all knowledge of the humans
philosophy ought to become “mathesis universalis.”
This ideal of mathesis universalis was actualized by him in his philosophical thought, only in mathematics, namely as analytic geometry.
2. discours de la méthode et les essais 1637 (The Preface to “Le Monde”)
a. Discours de la méthode
b. La dioptrique
c. Le météores
d. La géométrie
Since Descartes moved to Holland (1633), he almost completed an opus called Le Monde, which dealt with the knowledge of Nature and the universe. At that time, Galilei’s book, Dialogo sopra i due massimi sistemi del monde (1632) which compared Ptolemios’system with Copernicus’ was condemned by the authority of Rome (because Galilei defended Copernican heliocentric system of the universe). Since Descartes’ book was inseparably related to the heliocentric view of the universe, Descartes immediately abandoned the publication of Le Monde.
Descartes published the portion, b, c), and d) above, which was unrelated to the heliocentric view of universe in 1637 with the Preface (= a))he quickly wrote for this portion.
In this, Descartes presented in it his basic thought about science and philosophy with the special emphasis on method.
In the second part of Discours de la méthode, Descartes rephrased his 21 rules in Regulae into 4. b), c). d) are actual applications of the basic ideas stated in a) Discours to three concrete instances. Analytic Geometry was invented by Descartes. Newton assiduously studied Descartes’ Analytic Geometry. Some fragments of Le Monde may be found in his posthumous manuscripts.
3. Meditationes de prima philosophia (1641) (The Meditations of primary Philosophy)
This consists of 6 meditations. Before its publication, Descartes distributed the manuscripts to his friends and other scholars for their comments and criticisms and published them together with his own opus. They were 7 objectiones and Descartes’ responsiones, the major objections of which are by Hobbes, Gassendi and Arnauld.
4. Principia philosophiae (1644) (The Principle of Philosophy)
a) On the principles of human cognition
b) On the principles of material facts
c) On the visible universe (the Sun, the Planets and the fixed Stars)
d) On the Earth
Descartes intended to make a systematic presentation of the universe, and yet it was limited to the matter of principle
5. Traité des passions de l’àme´1649
the book came to exist in Descartes’ correspondences with Princess Elizabeth


Father of the Contemporary Western Philosophy
Descartes started philosophizing with DOUBT, while the Ancient Greek Philosophers started to WONDER (THAUMAZEN). In the Ancient times, there were no philosophical prejudices to doubt, nor tradition to fight against, while at the dawn of the Contemporary Europe, the philosopher had to doubt about everything that had been inherited, transmitted as truth by authority, and by tradition. The challenge to the authority of church
The universal doubt or the methodological doubt is epoch-making

Reflection ‹Self-Reflection = Introspection as the philosophical method
Hegel in his Vorlesungen über die Philosophie der Geschichte S. 33
“René Descartes ist in der Tat der wahrhafte Anfänger der modernen Philosophie, insofern sie das Denken zum Prinzip macht…..” (René Descartes is really the true starter of the Contemporary Philosophy, as long as its philosophy makes our thinking (i.e., the act of consciousness) the principle…)

The Starting point of Philosophizing = the fact of consciousness
What is evident, immediately given to consciousness
(clara et distincta idea)
Clarification and delimitation of the region of consciousness

The new establishment of Metaphysics
on the basis of Epistemology

=”the Way of Knowing determines the Way of Being!”

Biot, the mathematician called Descartes proles sine matre creata (the child created without mother).
Bergson said that the same may be said of philosophy, too.

The Epistemological Dualism reflects in Dualism of mind and matter
in self evident truth, which is immediately & indubitably given in consciousness
in mathematical and natural scientific truth which is given as a clear and distinct idea
The latter is implicit assumption to support the prima facie basis for the former, metaphysics.

A new foundation of knowledge is to be established by discarding the “old knowledge” and tradition
We are full of prejudices of which we are not clearly aware.
de omnibus dubitandum!(Let Us Doubt Everything!)
Everything that we had believed to be true can and has to be doubted, because it can be false or erroneous.

What does Descartes mean, when he said, “we may have been deceived?”
1) Does he mean that all the knowledge we possess be “synthetic?”
If so, we have to answer how the evil spirit could influence us to be deceived in mathematics (I) and God (II)?
The question is, according to Descartes, that the knowledge of mathematics and of God are analytic and not synthetic.
the challenge is that we are forced to decide whether he did not mean to doubt “mathematics” and “God” (seriously, at least) or
we must say that the Cartesian doubt is not based on the fallibility of the synthetic truth.

2) The content of the “intuition” (“cogito, ergo sum.”) is analytic truth or a synthetic truth.
a) It is analytic:1] depends on the nature of the Cartesian doubt based on the fallibility of the synthetic truth.
2] for the attribute “cogitatio” implies the existence of its substratum “ego”
b) It is synthetic: 1] depends upon the nature of the doubt which can be related to “analytic knowledge”, too.
2] the implication of “ego” from the attribute “cogitatio” is established after the ascertainment of “cogito, ergo sum” and not the reverse.

In Meditations,
Descartes doubts 1) sense-perception
2) natural sciences
3) physics
4) mathematics
5) the Existence of God

II. Cogito, ergo sum (=the proof of the existence of mind)
a) I doubt that the world is as it reveals itself to me.
b) I doubt that God exists
c) I doubt that the things other than I exists
d) I doubt that I possess my own body
e) I doubt that 2+3 =5

The Only fact I cannot doubt is the fact that I am doubting everything.
The only point which doubt cannot be directed
= the existence of ego as the agent of my cogitatio

In doubting, I exist.

To be deceived = to represent an erroneous “idea.”
in any event,
I am representing something.
This representing itself can not be doubted (cannot be nullified.)
The content of intention, the content of our consciousness may be false, but
The act of consciousness itself cannot be doubted. It must be there to falsify its intention.

Against “Cogito, ergo sum.” to be the First Principle, Arnould objected as follows:
There must be the following syllogism whose Major Premiss is omitted.
All thinking things are existing
I am a thinking thing
Therefore, I am existing. (cf. Principia Philosophiae I-XLIX)

Descartes repudiated Arnould’s criticism by saying
We must immediately experience that we exist as a thinking thing.
It is not a logical inference, as Arnould reformulated it.
This is an indubitable, self-evident Intuition.

Thus Prior to anything,
“Cogito, ergo sum.” is the First Principle.

“Tanquam rem per se notam simplici mentis intuitu agnoscit.”
(We recognize by a simple intuition of mind as if it were known by itself.)

“Apud se experiatur, fieri non possa ut cogitet, nisi existat.”
(We experience in oneself that we could not think without existing.)

In us,
Being and Thinking are one and the same!

In other words,
One’s Existence (=Existence of Mind) consists in no other than Thinking.

III. Clear and Distinct Knowledge (The Criteria of Truth)

Omne est verum, quod clare et distincte percipio.” (Meditationes III & IV)
(Everything is true that is clearly and distinctly perceived.)

“Clara est perceptio quae menti attendi praesens et apart est.”
(The perception is clear that is present and apart to the attentive mind.)

“Distincta est perceptio quae, cum clara ist, ab omnibus aliis ita sejuncta est et paecisa, ut nihil plane aliud, quam quod clarum est, in se contneat.”
(The perception is distinct that being clear, is articulated from everything else and precise and does not contain in itself nothing which is not clear.)

To Montaigne, who was a skeptic,
Doubt is the final stage of his philosophical inquiry.

To Descartes,
Doubt, which is methodological and is often called the universal doubt, stands at the beginning of his inquiry.

The model of clear and distinct knowledge may be best found in mathematical truth.

It is not so clear if the clear and distinct knowledge is by its nature self-evident, apodictic.
At least, those fundamental principles and axioms are to be apodictic.

IV. The Existence of God and the existence of matter

(i) Descartes’ own aposteriori proof of the Existence of God.
This is a modification of the Cosmological Argument for the Existence of God
1. The demonstration starts with the fact that I possess the Idea of God.

2. There are three kinds of ideas
Ideae innatae (universals, truth, thinking) = clear and distinct
Ideae adventitiae (sound, sun, heat, etc.)
Ideae a me ipso fictate (unicorn, pink elephant)

3. by means of the method of elimination,
The Idea of God is not an adventitious idea that is neither clear nor distinct (= the Idea of God does not come through senses)
The Idea of God is not a fictitious idea that is created by combining more than one adventitious ideas = neither clear nor distinct.
The Idea of God being clear and distinct must be an innate Idea

4. ex nihilo nihil fit. (Nothing comes out of nothing. Everything has its cause to exist.)

All ideas have their own cause, i.e., All ideas are ideas of something (=object of an idea)

the reality (= perfection) of the cause „ the reality (perfection) of the effect

Descartes uses the distinction between
realitas formalis
realitas objectiva (sive repraesentativa)
the formal reality means the being (reality means perfection as well) of the object itself, or the thing itself
(= God Himself in this case)
the objective reality means the being (reality means perfection as well) of the idea or representation (in the consciousness) of the object
(= The Idea of God in me)
Needless to say,
the reality or being of infinity (God Himself) > the reality or being of finite
(My Idea of God)
The imperfection of ourselves is known in contrast to the perfection of God.

4. The Idea of God (which we possess, does not represent his perfection in every respect) is sufficient to reveal the Existence of God.

(ii). the A priori Proof of the Existence of God (Anselm’s ontological argument)
The Essence (Perfect) of God necessarily implies His Existence as a part of His Perfect Essence.

God is the only being which is cause sui, i.e., the Self Caused Cause, while we are not.
In this sense, God is the only substance (i.e., the Infinite Substance),
while the two finite substances, i.e., mind and matter, are finite substances.
(iii). The A posteriori Proof II (A modified Cosmological Proof)
Although God created (caused) us to exist, but only as finite beings (which, being finite, need the cause for the existence, while God as causa sui caused and is causing Himself to exist)
Among the beings which are finite,
that I am, i.e., exist now, does not necessarily imply that I will continue to exist at the next moment. At every new moment, I would not exist, or God could make me perish.
Unless God exists as the cause of my existence at every minute, I could be nothing, but I am.
Therefore, God must exist as the cause of all the creatures for their being.

V. Veracitas Dei(God’s Veracity)
God’s Truthfulness is a part of God’s Perfection (which is a self-evident truth.)

As to the existence of the external world ( including all material substances),
according Descartes,
God cannot deceive us, because otherwise He is Imperfect! (Evil is a defective form)
God is in fact truthful, so
the external world necessarily exists or the material substances must exist.
(as a corollary, other minds as spiritual substances also necessarily exist!)

The certainty = ratio cogniscendi for God’s existence

God’s existence = ratio essendi for the certainty

God fuctions as 1. the proof for the certainty of mathematical truths
2. the bridge for solipsism to the external world

VI. Substance, Attribute and Modes

Certain ideas represent “facts” (things themselves?) = substances
Other ideas represent their “essential characters” = attributes
Other ideas represent their “accidental qualities or characters” = modes

Substance = res quae ita existit, ut nulla alia re indigeat ad existendum.(Principia I, 51)
(the thing which exists and does not need anything else for its existence.)

Attribute = represent the essential nature of a substance (e.g., extension and thinking)
and can be understood without a reference to anything else.
We recognize the attribute and infer the existence of the substance.

= the secondary characteristic only by means of the attribute.

The Cartesian notion of substance played the central theme of philosophical inquiry until Hume.

Substances Attributes Modes
Infinite Substance = Deus
finite substances
Mens = res cogitans cogitatio perceive, will, reason, imagine
(Mind=thinking thing) (thinking)
Materia = res extensa extensio shape, weight, place, motion
(Matter=extended thing)(extension)

In the universe, according to Descartes,
there are two completely distinct, mutually irreducible (finite) substances, i.e.,
res cogitans
res extensa that which is comprehensible by mathematics and mathematization

This dualism will have an enormous implications to the further development of philosophy and sciences in the West.

Religious beliefs
Theism in the narrower sense

VII. Philosophy of Nature

Matter = material substance which can only be comprehensible mathematico-mechanistically

Apud me omnia flunt mathematrice in natura
(Everything is made mathematically to me.)

We all possess sense organs
We perceive an object through senses, they are neither clear nor distinct. What is sensed is how the external reality is to appear to us. there therefore, there is a distinction between reality and appearance.

Descartes distinguished the appearance of an object
its reality.

It is a common error to take the appearance for reality.

In consequence,
Descartes also accepted the distinction between the primary qualities
the secondary qualities

The Essence of Matter = extensio = Spatial quantity.
corpus est extensio sive spatium.

The interesting thing is that
extension is so-to-speak a mathematical body
matter is a physical body
This distinction is of course only in ideas (in representations)

Matter is infinite
= Space
which is neither finite to the external
nor finite to the internal.
infinitely divisible
There is no such a thing as an atom (the indivisible).

What really is a relatively small particles such as copuscula (=molecules).

the universe is infinite, limitless.

According to Descartes,
there is only one material substance (Henism =the doctrine holding only one being)
many material substances are modi of this one res extensa

While in the spirits, there are many individual minds,
in the natural world, there is only one Matter.


Matter is the quantity which can be divided,
formed into a shape and

Motion is merely change of a matter from one place to another.
(Leibniz recognized the primordial power in motion)

To be in motion or to be in station is simply two different states of matter.

Any motion is relative. However,
the ultimate cause of motion is God.

the law of inertia
1) According to Descartes, matter has the power only in the meaning of the matter tendency or potency to either keep moving straight or stationing.

Descartes held the constancy of the quantity of movement (m.v) = velocity
Leibniz held that the constancy of the live force (force vive) or force (m.v2)

2) an object doing a circular motion is caused therefore by some external cause.

Descartes based these two laws on the immutability and simplicity of God.

3) transmission of motion
when the two object collide, if their motion differ, the stronger motion will be transmitted to the weaker.

On the basis of this law, there is an understanding that motion itself is distinct from its direction.

According to Descartes, matter does not have any power. Any alteration of matter is due to the external cause.


Anything else which cannot be explained by “solid body” is explained by the combination of solid and liquid.

the universe is filled with “fluid” in vortex.

heliocentric view of the universe ?

The evolution of the universe

Mechanistic theory of nature

matter is a huge machine

No mind in animals
Only spiritus animalis

the communication of mind and body is at the glans pinealis.

The mind and body problem

due to Descartes’s separation of mind from matter and view of human body as a pure sophisticated machine, there arises the famous mind-body problem in metaphysics

human body and animal are highly sophisticated machines
humans possess language,
the motion from reason
possess spirit = rational mind (anima rationalis)


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