René Descartes (, UK also ; French: [ʁəne
dekaʁt]; Latinized: Renatus Cartesius; adjectival
form: "Cartesian"; 31 March 1596 – 11 February
1650) was a French philosopher, mathematician,
and scientist.
A native of the Kingdom of France, he spent
about 20 years (1629–49) of his life in
the Dutch Republic after serving for a while
in the Dutch States Army of Maurice of Nassau,
Prince of Orange and the Stadtholder of the
United Provinces.
He is generally considered one of the most
notable intellectual figures of the Dutch
Golden Age.Descartes' Meditations on First
Philosophy (1641) continues to be a standard
text at most university philosophy departments.
Descartes' influence in mathematics is equally
apparent; the Cartesian coordinate system
(see below) was named after him.
He is credited as the father of analytical
geometry, the bridge between algebra and geometry,
used in the discovery of infinitesimal calculus
and analysis.
Descartes was also one of the key figures
in the Scientific Revolution.
Descartes refused to accept the authority
of previous philosophers.
He frequently set his views apart from those
of his predecessors.
In the opening section of the Passions of
the Soul, an early modern treatise on emotions,
Descartes goes so far as to assert that he
will write on this topic "as if no one had
written on these matters before".
His best known philosophical statement is
"I think, therefore I am" (French: Je pense,
donc je suis; Latin: Ego cogito, ergo sum),
found in Discourse on the Method (1637; written
in French and Latin) and Principles of Philosophy
(1644; written in Latin).Many elements of
his philosophy have precedents in late Aristotelianism,
the revived Stoicism of the 16th century,
or in earlier philosophers like Augustine.
In his natural philosophy, he differed from
the schools on two major points: first, he
rejected the splitting of corporeal substance
into matter and form; second, he rejected
any appeal to final ends, divine or natural,
in explaining natural phenomena.
In his theology, he insists on the absolute
freedom of God's act of creation.
Descartes laid the foundation for 17th-century
continental rationalism, later advocated by
Spinoza and Leibniz, and opposed by the empiricist
school of thought consisting of Hobbes, Locke,
Berkeley, and Hume.
Leibniz, Spinoza, and Descartes were all well
versed in mathematics as well as philosophy,
and Descartes and Leibniz contributed greatly
to science as well.
== Life ==
=== 
Early life ===
René Descartes was born in La Haye en Touraine
(now Descartes, Indre-et-Loire), France, on
31 March 1596.
His mother, Jeanne Brochard, died soon after
giving birth to him, and so he was not expected
to survive.
Descartes' father, Joachim, was a member of
the Parlement of Brittany at Rennes.
René lived with his grandmother and with
his great-uncle.
Although the Descartes family was Roman Catholic,
the Poitou region was controlled by the Protestant
Huguenots.
In 1607, late because of his fragile health,
he entered the Jesuit Collège Royal Henry-Le-Grand
at La Flèche, where he was introduced to
mathematics and physics, including Galileo's
work.
After graduation in 1614, he studied for two
years (1615–16) at the University of Poitiers,
earning a Baccalauréat and Licence in canon
and civil law in 1616, in accordance with
his father's wishes that he should become
a lawyer.
From there he moved to Paris.
In Discourse on the Method, Descartes recalls,
I entirely abandoned the study of letters.
Resolving to seek no knowledge other than
that of which could be found in myself or
else in the great book of the world, I spent
the rest of my youth traveling, visiting courts
and armies, mixing with people of diverse
temperaments and ranks, gathering various
experiences, testing myself in the situations
which fortune offered me, and at all times
reflecting upon whatever came my way so as
to derive some profit from it.
Given his ambition to become a professional
military officer, in 1618, Descartes joined,
as a mercenary, the Protestant Dutch States
Army in Breda under the command of Maurice
of Nassau, and undertook a formal study of
military engineering, as established by Simon
Stevin.
Descartes, therefore, received much encouragement
in Breda to advance his knowledge of mathematics.
In this way, he became acquainted with Isaac
Beeckman, the principal of a Dordrecht school,
for whom he wrote the Compendium of Music
(written 1618, published 1650).
Together they worked on free fall, catenary,
conic section, and fluid statics.
Both believed that it was necessary to create
a method that thoroughly linked mathematics
and physics.While in the service of the Catholic
Duke Maximilian of Bavaria since 1619, Descartes
was present at the Battle of the White Mountain
outside Prague, in November 1620.
=== Visions ===
According to Adrien Baillet, on the night
of 10–11 November 1619 (St. Martin's Day),
while stationed in Neuburg an der Donau, Descartes
shut himself in a room with an "oven" (probably
a Kachelofen or masonry heater) to escape
the cold.
While within, he had three dreams and believed
that a divine spirit revealed to him a new
philosophy.
However, it is likely that what Descartes
considered to be his second dream was actually
an episode of exploding head syndrome.
Upon exiting, he had formulated analytical
geometry and the idea of applying the mathematical
method to philosophy.
He concluded from these visions that the pursuit
of science would prove to be, for him, the
pursuit of true wisdom and a central part
of his life's work.
Descartes also saw very clearly that all truths
were linked with one another so that finding
a fundamental truth and proceeding with logic
would open the way to all science.
Descartes discovered this basic truth quite
soon: his famous "I think, therefore I am".
=== France ===
In 1620 Descartes left the army.
He visited Basilica della Santa Casa in Loreto,
then visited various countries before returning
to France, and during the next few years spent
time in Paris.
It was there that he composed his first essay
on method: Regulae ad Directionem Ingenii
(Rules for the Direction of the Mind).
He arrived in La Haye in 1623, selling all
of his property to invest in bonds, which
provided a comfortable income for the rest
of his life.
Descartes was present at the siege of La Rochelle
by Cardinal Richelieu in 1627.
In the fall of the same year, in the residence
of the papal nuncio Guidi di Bagno, where
he came with Mersenne and many other scholars
to listen to a lecture given by the alchemist
Nicolas de Villiers, Sieur de Chandoux on
the principles of a supposed new philosophy,
Cardinal Bérulle urged him to write an exposition
of his own new philosophy in some location
beyond the reach of the inquisition.
=== Netherlands ===
Descartes returned to the Dutch Republic in
1628.
In April 1629 he joined the University of
Franeker, studying under Adriaan Metius, living
either with a Catholic family, or renting
the Sjaerdemaslot, where he invited in vain
a French cook and an optician.
The next year, under the name "Poitevin",
he enrolled at the Leiden University to study
mathematics with Jacobus Golius, who confronted
him with Pappus's hexagon theorem, and astronomy
with Martin Hortensius.
In October 1630 he had a falling-out with
Beeckman, whom he accused of plagiarizing
some of his ideas.
In Amsterdam, he had a relationship with a
servant girl, Helena Jans van der Strom, with
whom he had a daughter, Francine, who was
born in 1635 in Deventer.
She died of scarlet fever at the age of 5.
Unlike many moralists of the time, Descartes
was not devoid of passions but rather defended
them; he wept upon Francine's death in 1640.
"Descartes said that he did not believe that
one must refrain from tears to prove oneself
a man."
Russell Shorto postulated that the experience
of fatherhood and losing a child formed a
turning point in Descartes' work, changing
its focus from medicine to a quest for universal
answers.Despite frequent moves, he wrote all
his major work during his 20-plus years in
the Netherlands, where he managed to revolutionize
mathematics and philosophy.
In 1633, Galileo was condemned by the Italian
Inquisition, and Descartes abandoned plans
to publish Treatise on the World, his work
of the previous four years.
Nevertheless, in 1637 he published part of
this work in three essays: "Les Météores"
(The Meteors), "La Dioptrique" (Dioptrics)
and "La Géométrie" (Geometry), preceded
by an introduction, his famous Discours de
la méthode (Discourse on the Method).
In it, Descartes lays out four rules of thought,
meant to ensure that our knowledge rests upon
a firm foundation.
The first was never to accept anything for
true which I did not clearly know to be such;
that is to say, carefully to avoid precipitancy
and prejudice, and to comprise nothing more
in my judgment than what was presented to
my mind so clearly and distinctly as to exclude
all ground of doubt.
In La Géométrie, Descartes exploited the
discoveries he made with Pierre de Fermat,
having been able to do so because his paper,
Introduction to Loci, was published posthumously
in 1679.
This later became known as Cartesian Geometry.
Descartes continued to publish works concerning
both mathematics and philosophy for the rest
of his life.
In 1641 he published a metaphysics work, Meditationes
de Prima Philosophia (Meditations on First
Philosophy), written in Latin and thus addressed
to the learned.
It was followed, in 1644, by Principia Philosophiæ
(Principles of Philosophy), a kind of synthesis
of the Discourse on the Method and Meditations
on First Philosophy.
In 1643, Cartesian philosophy was condemned
at the University of Utrecht, and Descartes
was obliged to flee to the Hague, and settled
in Egmond-Binnen.
Descartes began (through Alfonso Polloti,
an Italian general in Dutch service) a long
correspondence with Princess Elisabeth of
Bohemia, devoted mainly to moral and psychological
subjects.
Connected with this correspondence, in 1649
he published Les Passions de l'âme (Passions
of the Soul), that he dedicated to the Princess.
In 1647, he was awarded a pension by King
Louis XIV of France, though it was never paid.
A French translation of Principia Philosophiæ,
prepared by Abbot Claude Picot, was published
in 1647.
This edition Descartes also dedicated to Princess
Elisabeth.
In the preface to the French edition, Descartes
praised true philosophy as a means to attain
wisdom.
He identifies four ordinary sources to reach
wisdom and finally says that there is a fifth,
better and more secure, consisting in the
search for first causes.
=== Sweden ===
By 1649, Descartes had become famous throughout
Europe for being one of the continent's greatest
philosophers and scientists.
That year, Queen Christina of Sweden invited
Descartes to her court to organize a new scientific
academy and tutor her in his ideas about love.
She was interested in and stimulated Descartes
to publish the "Passions of the Soul", a work
based on his correspondence with Princess
Elisabeth.
Descartes accepted, and moved to Sweden in
the middle of winter.He was a guest at the
house of Pierre Chanut, living on Västerlånggatan,
less than 500 meters from Tre Kronor in Stockholm.
There, Chanut and Descartes made observations
with a Torricellian barometer, a tube with
mercury.
Challenging Blaise Pascal, Descartes took
the first set of barometric readings in Stockholm
to see if atmospheric pressure could be used
in forecasting the weather.
=== Death ===
Descartes apparently started giving lessons
to Queen Christina after her birthday, three
times a week, at 5 a.m, in her cold and draughty
castle.
Soon it became clear they did not like each
other; she did not like his mechanical philosophy,
nor did he appreciate her interest in Ancient
Greek.
By 15 January 1650, Descartes had seen Christina
only four or five times.
On 1 February he contracted pneumonia and
died on 11 February.
The cause of death was pneumonia according
to Chanut, but peripneumonia according to
the doctor Van Wullen who was not allowed
to bleed him.
(The winter seems to have been mild, except
for the second half of January which was harsh
as described by Descartes himself; however,
"this remark was probably intended to be as
much Descartes' take on the intellectual climate
as it was about the weather.")
In 1996 E. Pies, a German scholar, published
a book questioning this account, based on
a letter by Johann van Wullen, who had been
sent by Christina to treat him, something
Descartes refused, and more arguments against
its veracity have been raised since.
Descartes might have been assassinated as
he asked for an emetic: wine mixed with tobacco.As
a Catholic in a Protestant nation, he was
interred in a graveyard used mainly for orphans
in Adolf Fredriks kyrka in Stockholm.
His manuscripts came into the possession of
Claude Clerselier, Chanut's brother-in-law,
and "a devout Catholic who has begun the process
of turning Descartes into a saint by cutting,
adding and publishing his letters selectively."
In 1663, the Pope placed his works on the
Index of Prohibited Books.
In 1666 his remains were taken to France and
buried in the Saint-Étienne-du-Mont.
In 1671 Louis XIV prohibited all the lectures
in Cartesianism.
Although the National Convention in 1792 had
planned to transfer his remains to the Panthéon,
he was reburied in the Abbey of Saint-Germain-des-Prés
in 1819, missing a finger and skull.
His skull is on display in the Musée de l'Homme
in Paris.
== Philosophical work ==
Initially, Descartes arrives at only a single
first principle: I think.
Thought cannot be separated from me, therefore,
I exist (Discourse on the Method and Principles
of Philosophy).
Most famously, this is known as cogito ergo
sum (English: "I think, therefore I am").
Therefore, Descartes concluded, if he doubted,
then something or someone must be doing the
doubting, therefore the very fact that he
doubted proved his existence.
"The simple meaning of the phrase is that
if one is skeptical of existence, that is
in and of itself proof that he does exist."
These two first principles—I think and I
exist—were later confirmed by Descartes's
clear and distinct perception (delineated
in his Third Meditation): that I clearly and
distinctly perceive these two principles,
Descartes reasoned, ensures their indubitability.
Descartes concludes that he can be certain
that he exists because he thinks.
But in what form?
He perceives his body through the use of the
senses; however, these have previously been
unreliable.
So Descartes determines that the only indubitable
knowledge is that he is a thinking thing.
Thinking is what he does, and his power must
come from his essence.
Descartes defines "thought" (cogitatio) as
"what happens in me such that I am immediately
conscious of it, insofar as I am conscious
of it".
Thinking is thus every activity of a person
of which the person is immediately conscious.
He gave reasons for thinking that waking thoughts
are distinguishable from dreams, and that
one's mind cannot have been "hijacked" by
an evil demon placing an illusory external
world before one's senses.
And so something that I thought I was seeing
with my eyes is in fact grasped solely by
the faculty of judgment which is in my mind.
In this manner, Descartes proceeds to construct
a system of knowledge, discarding perception
as unreliable and, instead, admitting only
deduction as a method.
=== Dualism ===
Descartes, influenced by the automatons on
display throughout the city of Paris, began
to investigate the connection between the
mind and body, and how the two interact.
His main influences for dualism were theology
and physics.
The theory on the dualism of mind and body
is Descartes' signature doctrine and permeates
other theories he advanced.
Known as Cartesian dualism (or Mind-Body Dualism),
his theory on the separation between the mind
and the body went on to influence subsequent
Western philosophies.
In Meditations on First Philosophy, Descartes
attempted to demonstrate the existence of
God and the distinction between the human
soul and the body.
Humans are a union of mind and body; thus
Descartes' dualism embraced the idea that
mind and body are distinct but closely joined.
While many contemporary readers of Descartes
found the distinction between mind and body
difficult to grasp, he thought it was entirely
straightforward.
Descartes employed the concept of modes, which
are the ways in which substances exist.
In Principles of Philosophy, Descartes explained,
"we can clearly perceive a substance apart
from the mode which we say differs from it,
whereas we cannot, conversely, understand
the mode apart from the substance".
To perceive a mode apart from its substance
requires an intellectual abstraction, which
Descartes explained as follows:
The intellectual abstraction consists in my
turning my thought away from one part of the
contents of this richer idea the better to
apply it to the other part with greater attention.
Thus, when I consider a shape without thinking
of the substance or the extension whose shape
it is, I make a mental abstraction.
According to Descartes two substances are
really distinct when each of them can exist
apart from the other.
Thus Descartes reasoned that God is distinct
from humans, and the body and mind of a human
are also distinct from one another.
He argued that the great differences between
body (an extended thing) and mind (an un-extended,
immaterial thing) make the two ontologically
distinct.
But that the mind was utterly indivisible:
because "when I consider the mind, or myself
in so far as I am merely a thinking thing,
I am unable to distinguish any part within
myself; I understand myself to be something
quite single and complete."In Meditations
Descartes discussed a piece of wax and exposed
the single most characteristic doctrine of
Cartesian dualism: that the universe contained
two radically different kinds of substances—the
mind or soul defined as thinking, and the
body defined as matter and unthinking.
The Aristotelian philosophy of Descartes'
days held that the universe was inherently
purposeful or theological.
Everything that happened, be it the motion
of the stars or the growth of a tree, was
supposedly explainable by a certain purpose,
goal or end that worked its way out within
nature.
Aristotle called this the "final cause", and
these final causes were indispensable for
explaining the ways nature operated.
With his theory on dualism Descartes fired
the opening shot for the battle between the
traditional Aristotelian science and the new
science of Kepler and Galileo which denied
the final cause for explaining nature.
Descartes' dualism provided the philosophical
rationale for the latter and he expelled the
final cause from the physical universe (or
res extensa).
For Descartes the only place left for the
final cause was the mind (or res cogitans).
Therefore, while Cartesian dualism paved the
way for modern physics, it also held the door
open for religious beliefs about the immortality
of the soul.Descartes' dualism of mind and
matter implied a concept of human beings.
A human was according to Descartes a composite
entity of mind and body.
Descartes gave priority to the mind and argued
that the mind could exist without the body,
but the body could not exist without the mind.
In Meditations Descartes even argues that
while the mind is a substance, the body is
composed only of "accidents".
But he did argue that mind and body are closely
joined:
Nature also teaches me, by the sensations
of pain, hunger, thirst and so on, that I
am not merely present in my body as a pilot
in his ship, but that I am very closely joined
and, as it were, intermingled with it, so
that I and the body form a unit.
If this were not so, I, who am nothing but
a thinking thing, would not feel pain when
the body was hurt, but would perceive the
damage purely by the intellect, just as a
sailor perceives by sight if anything in his
ship is broken.
Descartes' discussion on embodiment raised
one of the most perplexing problems of his
dualism philosophy: What exactly is the relationship
of union between the mind and the body of
a person?
Therefore, Cartesian dualism set the agenda
for philosophical discussion of the mind–body
problem for many years after Descartes' death.
Descartes was also a rationalist and believed
in the power of innate ideas.
Descartes argued the theory of innate knowledge
and that all humans were born with knowledge
through the higher power of God.
It was this theory of innate knowledge that
later led philosopher John Locke (1632–1704)
to combat the theory of empiricism, which
held that all knowledge is acquired through
experience.
=== Descartes on physiology and psychology
===
In The Passions of the Soul written between
1645 and 1646 Descartes discussed the common
contemporary belief that the human body contained
animal spirits.
These animal spirits were believed to be light
and roaming fluids circulating rapidly around
the nervous system between the brain and the
muscles, and served as a metaphor for feelings,
like being in high or bad spirit.
These animal spirits were believed to affect
the human soul, or passions of the soul.
Descartes distinguished six basic passions:
wonder, love, hatred, desire, joy and sadness.
All of these passions, he argued, represented
different combinations of the original spirit,
and influenced the soul to will or want certain
actions.
He argued, for example, that fear is a passion
that moves the soul to generate a response
in the body.
In line with his dualist teachings on the
separation between the soul and the body,
he hypothesized that some part of the brain
served as a connector between the soul and
the body and singled out the pineal gland
as connector.
Descartes argued that signals passed from
the ear and the eye to the pineal gland, through
animal spirits.
Thus different motions in the gland cause
various animal spirits.
He argued that these motions in the pineal
gland are based on God's will and that humans
are supposed to want and like things that
are useful to them.
But he also argued that the animal spirits
that moved around the body could distort the
commands from the pineal gland, thus humans
had to learn how to control their passions.Descartes
advanced a theory on automatic bodily reactions
to external events which influenced 19th-century
reflex theory.
He argued that external motions such as touch
and sound reach the endings of the nerves
and affect the animal spirits.
Heat from fire affects a spot on the skin
and sets in motion a chain of reactions, with
the animal spirits reaching the brain through
the central nervous system, and in turn animal
spirits are sent back to the muscles to move
the hand away from the fire.
Through this chain of reactions the automatic
reactions of the body do not require a thought
process.Above all he was among the first scientists
who believed that the soul should be subject
to scientific investigation.
He challenged the views of his contemporaries
that the soul was divine, thus religious authorities
regarded his books as dangerous.
Descartes' writings went on to form the basis
for theories on emotions and how cognitive
evaluations were translated into affective
processes.
Descartes believed that the brain resembled
a working machine and unlike many of his contemporaries
believed that mathematics and mechanics could
explain the most complicated processes of
the mind.
In the 20th century Alan Turing advanced computer
science based on mathematical biology as inspired
by Descartes.
His theories on reflexes also served as the
foundation for advanced physiological theories
more than 200 years after his death.
The physiologist Ivan Pavlov was a great admirer
of Descartes.
=== Descartes' moral philosophy ===
For Descartes, ethics was a science, the highest
and most perfect of them.
Like the rest of the sciences, ethics had
its roots in metaphysics.
In this way, he argues for the existence of
God, investigates the place of man in nature,
formulates the theory of mind-body dualism,
and defends free will.
However, as he was a convinced rationalist,
Descartes clearly states that reason is sufficient
in the search for the goods that we should
seek, and virtue consists in the correct reasoning
that should guide our actions.
Nevertheless, the quality of this reasoning
depends on knowledge, because a well-informed
mind will be more capable of making good choices,
and it also depends on mental condition.
For this reason, he said that a complete moral
philosophy should include the study of the
body.
He discussed this subject in the correspondence
with Princess Elisabeth of Bohemia, and as
a result wrote his work The Passions of the
Soul, that contains a study of the psychosomatic
processes and reactions in man, with an emphasis
on emotions or passions.
His works about human passion and emotion
would be the basis for the philosophy of his
followers (see Cartesianism), and would have
a lasting impact on ideas concerning what
literature and art should be, specifically
how it should invoke emotion.Humans should
seek the sovereign good that Descartes, following
Zeno, identifies with virtue, as this produces
a solid blessedness or pleasure.
For Epicurus the sovereign good was pleasure,
and Descartes says that, in fact, this is
not in contradiction with Zeno's teaching,
because virtue produces a spiritual pleasure,
that is better than bodily pleasure.
Regarding Aristotle's opinion that happiness
depends on the goods of fortune, Descartes
does not deny that this good contributes to
happiness but remarks that they are in great
proportion outside one's own control, whereas
one's mind is under one's complete control.
The moral writings of Descartes came at the
last part of his life, but earlier, in his
Discourse on the Method he adopted three maxims
to be able to act while he put all his ideas
into doubt.
This is known as his "Provisional Morals".
=== Descartes on religious beliefs ===
In the third and fifth Meditation, he offers
an ontological proof of a benevolent God (through
both the ontological argument and trademark
argument).
Because God is benevolent, he can have some
faith in the account of reality his senses
provide him, for God has provided him with
a working mind and sensory system and does
not desire to deceive him.
From this supposition, however, he finally
establishes the possibility of acquiring knowledge
about the world based on deduction and perception.
Regarding epistemology, therefore, he can
be said to have contributed such ideas as
a rigorous conception of foundationalism and
the possibility that reason is the only reliable
method of attaining knowledge.
He, nevertheless, was very much aware that
experimentation was necessary to verify and
validate theories.In his Meditations on First
Philosophy Descartes sets forth two proofs
for God's existence.
One of these is founded upon the possibility
of thinking the "idea of a being that is supremely
perfect and infinite," and suggests that "of
all the ideas that are in me, the idea that
I have of God is the most true, the most clear
and distinct."
Descartes considered himself to be a devout
Catholic and one of the purposes of the Meditations
was to defend the Catholic faith.
His attempt to ground theological beliefs
on reason encountered intense opposition in
his time, however: Pascal regarded Descartes'
views as rationalist and mechanist, and accused
him of deism: "I cannot forgive Descartes;
in all his philosophy, Descartes did his best
to dispense with God.
But Descartes could not avoid prodding God
to set the world in motion with a snap of
his lordly fingers; after that, he had no
more use for God," while a powerful contemporary,
Martin Schoock, accused him of atheist beliefs,
though Descartes had provided an explicit
critique of atheism in his Meditations.
The Catholic Church prohibited his books in
1663.Descartes also wrote a response to external
world scepticism.
Through this method of scepticism, he does
not doubt for the sake of doubting but to
achieve concrete and reliable information.
In other words, certainty.
He argues that sensory perceptions come to
him involuntarily, and are not willed by him.
They are external to his senses, and according
to Descartes, this is evidence of the existence
of something outside of his mind, and thus,
an external world.
Descartes goes on to show that the things
in the external world are material by arguing
that God would not deceive him as to the ideas
that are being transmitted, and that God has
given him the "propensity" to believe that
such ideas are caused by material things.
Descartes also believes a substance is something
that does not need any assistance to function
or exist.
Descartes further explains how only God can
be a true “substance”.
But minds are substances, meaning they need
only God for it to function.
The mind is a thinking substance.
The means for a thinking substance stem from
ideas.
=== Descartes and natural science ===
Descartes is often regarded as the first thinker
to emphasize the use of reason to develop
the natural sciences.
For him the philosophy was a thinking system
that embodied all knowledge, and expressed
it in this way:
Thus, all Philosophy is like a tree, of which
Metaphysics is the root, Physics the trunk,
and all the other sciences the branches that
grow out of this trunk, which are reduced
to three principals, namely, Medicine, Mechanics,
and Ethics.
By the science of Morals, I understand the
highest and most perfect which, presupposing
an entire knowledge of the other sciences,
is the last degree of wisdom.
In his Discourse on the Method, he attempts
to arrive at a fundamental set of principles
that one can know as true without any doubt.
To achieve this, he employs a method called
hyperbolical/metaphysical doubt, also sometimes
referred to as methodological scepticism:
he rejects any ideas that can be doubted and
then re-establishes them in order to acquire
a firm foundation for genuine knowledge.
Descartes built his ideas from scratch.
He relates this to architecture: the top soil
is taken away to create a new building or
structure.
Descartes calls his doubt the soil and new
knowledge the buildings.
To Descartes, Aristotle's foundationalism
is incomplete and his method of doubt enhances
foundationalism.
=== Descartes on animals ===
Descartes denied that animals had reason or
intelligence.
He argued that animals did not lack sensations
or perceptions, but these could be explained
mechanistically.
Whereas humans had a soul, or mind, and were
able to feel pain and anxiety, animals by
virtue of not having a soul could not feel
pain or anxiety.
If animals showed signs of distress then this
was to protect the body from damage, but the
innate state needed for them to suffer was
absent.
Although Descartes' views were not universally
accepted they became prominent in Europe and
North America, allowing humans to treat animals
with impunity.
The view that animals were quite separate
from humanity and merely machines allowed
for the maltreatment of animals, and was sanctioned
in law and societal norms until the middle
of the 19th century.
The publications of Charles Darwin would eventually
erode the Cartesian view of animals.
Darwin argued that the continuity between
humans and other species opened the possibilities
that animals did not have dissimilar properties
to suffer.
== Historical impact ==
=== Emancipation from Church doctrine ===
Descartes has often been dubbed the father
of modern Western philosophy, the thinker
whose approach has profoundly changed the
course of Western philosophy and set the basis
for modernity.
The first two of his Meditations on First
Philosophy, those that formulate the famous
methodic doubt, represent the portion of Descartes'
writings that most influenced modern thinking.
It has been argued that Descartes himself
didn't realize the extent of this revolutionary
move.
In shifting the debate from "what is true"
to "of what can I be certain?," Descartes
arguably shifted the authoritative guarantor
of truth from God to humanity (even though
Descartes himself claimed he received his
visions from God)—while the traditional
concept of "truth" implies an external authority,
"certainty" instead relies on the judgment
of the individual.
In an anthropocentric revolution, the human
being is now raised to the level of a subject,
an agent, an emancipated being equipped with
autonomous reason.
This was a revolutionary step that established
the basis of modernity, the repercussions
of which are still being felt: the emancipation
of humanity from Christian revelational truth
and Church doctrine; humanity making its own
law and taking its own stand.
In modernity, the guarantor of truth is not
God anymore but human beings, each of whom
is a "self-conscious shaper and guarantor"
of their own reality.
In that way, each person is turned into a
reasoning adult, a subject and agent, as opposed
to a child obedient to God.
This change in perspective was characteristic
of the shift from the Christian medieval period
to the modern period, a shift that had been
anticipated in other fields, and which was
now being formulated in the field of philosophy
by Descartes.This anthropocentric perspective
of Descartes' work, establishing human reason
as autonomous, provided the basis for the
Enlightenment's emancipation from God and
the Church.
According to Martin Heidegger, the perspective
of Descartes' work also provided the basis
for all subsequent anthropology.
Descartes' philosophical revolution is sometimes
said to have sparked modern anthropocentrism
and subjectivism.
=== Mathematical legacy ===
One of Descartes' most enduring legacies was
his development of Cartesian or analytic geometry,
which uses algebra to describe geometry.
He "invented the convention of representing
unknowns in equations by x, y, and z, and
knowns by a, b, and c".
He also "pioneered the standard notation"
that uses superscripts to show the powers
or exponents; for example, the 2 used in x2
to indicate x squared.
He was first to assign a fundamental place
for algebra in our system of knowledge, using
it as a method to automate or mechanize reasoning,
particularly about abstract, unknown quantities.
European mathematicians had previously viewed
geometry as a more fundamental form of mathematics,
serving as the foundation of algebra.
Algebraic rules were given geometric proofs
by mathematicians such as Pacioli, Cardan,
Tartaglia and Ferrari.
Equations of degree higher than the third
were regarded as unreal, because a three-dimensional
form, such as a cube, occupied the largest
dimension of reality.
Descartes professed that the abstract quantity
a2 could represent length as well as an area.
This was in opposition to the teachings of
mathematicians, such as Vieta, who argued
that it could represent only area.
Although Descartes did not pursue the subject,
he preceded Gottfried Wilhelm Leibniz in envisioning
a more general science of algebra or "universal
mathematics," as a precursor to symbolic logic,
that could encompass logical principles and
methods symbolically, and mechanize general
reasoning.Descartes' work provided the basis
for the calculus developed by Newton and Leibniz,
who applied infinitesimal calculus to the
tangent line problem, thus permitting the
evolution of that branch of modern mathematics.
His rule of signs is also a commonly used
method to determine the number of positive
and negative roots of a polynomial.
The beginning to Descartes' interest in physics
is accredited to the amateur scientist and
mathematician Isaac Beeckman, who was at the
forefront of a new school of thought known
as mechanical philosophy.
With this foundation of reasoning, Descartes
formulated many of his theories on mechanical
and geometrical physics.
Descartes discovered an early form of the
law of conservation of mechanical momentum
(a measure of the motion of an object), and
envisioned it as pertaining to motion in a
straight line, as opposed to perfect circular
motion, as Galileo had envisioned it.
He outlined his views on the universe in his
Principles of Philosophy.
Descartes also made contributions to the field
of optics.
He showed by using geometric construction
and the law of refraction (also known as Descartes'
law or more commonly Snell's law) that the
angular radius of a rainbow is 42 degrees
(i.e., the angle subtended at the eye by the
edge of the rainbow and the ray passing from
the sun through the rainbow's centre is 42°).
He also independently discovered the law of
reflection, and his essay on optics was the
first published mention of this law.
=== Influence on Newton's mathematics ===
Current opinion is that Descartes had the
most influence of anyone on the young Newton,
and this is arguably one of Descartes' most
important contributions.
Newton continued Descartes' work on cubic
equations, which freed the subject from the
fetters of the Greek perspectives.
The most important concept was his very modern
treatment of independent variables.
=== Contemporary reception ===
Although Descartes was well known in academic
circles towards the end of his life, the teaching
of his works in schools was controversial.
Henri de Roy (Henricus Regius, 1598–1679),
Professor of Medicine at the University of
Utrecht, was condemned by the Rector of the
University, Gijsbert Voet (Voetius), for teaching
Descartes' physics.
== Legacy ==
Mathematical concepts named after DescartesCartesian
circle
Cartesian coordinate system
Cartesian diagram
Cartesian diver
Cartesian morphism
Cartesian plane
Cartesian product
Cartesian product of graphs
Cartesian theater
Cartesian tree
Descartes' rule of signs
Descartes' theorem (4 tangent circles)
Descartes' theorem (on total angular defect)
Folium of DescartesOtherCartesian doubt
3587 Descartes, asteroid
Cartesian materialism (not a view that was
held by or formulated by Descartes)
Paris Descartes University
== Writings ==
1618.
Musicae Compendium.
A treatise on music theory and the aesthetics
of music written for Descartes' early collaborator,
Isaac Beeckman (first posthumous edition 1650).
1626–1628.
Regulae ad directionem ingenii (Rules for
the Direction of the Mind).
Incomplete.
First published posthumously in Dutch translation
in 1684 and in the original Latin at Amsterdam
in 1701 (R. Des-Cartes Opuscula Posthuma Physica
et Mathematica).
The best critical edition, which includes
the Dutch translation of 1684, is edited by
Giovanni Crapulli (The Hague: Martinus Nijhoff,
1966).
1630–1631.
La recherche de la vérité par la lumière
naturelle (The Search for Truth) unfinished
dialogue published in 1701.
1630–1633.
Le Monde (The World) and L'Homme (Man).
Descartes' first systematic presentation of
his natural philosophy.
Man was published posthumously in Latin translation
in 1662; and The World posthumously in 1664.
1637.
Discours de la méthode (Discourse on the
Method).
An introduction to the Essais, which include
the Dioptrique, the Météores and the Géométrie.
1637.
La Géométrie (Geometry).
Descartes' major work in mathematics.
There is an English translation by Michael
Mahoney (New York: Dover, 1979).
1641.
Meditationes de prima philosophia (Meditations
on First Philosophy), also known as Metaphysical
Meditations.
In Latin; a second edition, published the
following year, included an additional objection
and reply, and a Letter to Dinet.
A French translation by the Duke of Luynes,
probably done without Descartes' supervision,
was published in 1647.
Includes six Objections and Replies.
1644.
Principia philosophiae (Principles of Philosophy),
a Latin textbook at first intended by Descartes
to replace the Aristotelian textbooks then
used in universities.
A French translation, Principes de philosophie
by Claude Picot, under the supervision of
Descartes, appeared in 1647 with a letter-preface
to Princess Elisabeth of Bohemia.
1647.
Notae in programma (Comments on a Certain
Broadsheet).
A reply to Descartes' one-time disciple Henricus
Regius.
1648.
La description du corps humain (The Description
of the Human Body).
Published posthumously by Clerselier in 1667.
1648.
Responsiones Renati Des Cartes...
(Conversation with Burman).
Notes on a Q&A session between Descartes and
Frans Burman on 16 April 1648.
Rediscovered in 1895 and published for the
first time in 1896.
An annotated bilingual edition (Latin with
French translation), edited by Jean-Marie
Beyssade, was published in 1981 (Paris: PUF).
1649.
Les passions de l'âme (Passions of the Soul).
Dedicated to Princess Elisabeth of the Palatinate.
1657.
Correspondance (three volumes: 1657, 1659,
1667).
Published by Descartes' literary executor
Claude Clerselier.
The third edition, in 1667, was the most complete;
Clerselier omitted, however, much of the material
pertaining to mathematics.In January 2010,
a previously unknown letter from Descartes,
dated 27 May 1641, was found by the Dutch
philosopher Erik-Jan Bos when browsing through
Google.
Bos found the letter mentioned in a summary
of autographs kept by Haverford College in
Haverford, Pennsylvania.
The college was unaware that the letter had
never been published.
This was the third letter by Descartes found
in the last 25 years.
== See also ==
== Notes
