By Individual Philosopher > John Locke

Introduction

John Locke (1632 - 1704) was an English philosopher of the Age of Reason and early Age of Enlightenment. His ideas had enormous influence on the development of Epistemology and Political Philosophy, and he is widely regarded as one of the most influential early Enlightenment thinkers.
He is usually considered the first of the British Empiricists, the movement which included George Berkeley and David Hume, and which provided the mainopposition to the 17th Century Continental Rationalists. He argued that all of our ideas are ultimately derived from experience, and the knowledge of which we are capable is therefore severely limited in its scope and certainty.
His Philosophy of Mind is often cited as the origin for modern conceptions ofidentity and "the self". He also postulated, contrary to Cartesian and Christianphilosophy, that the mind was a "tabula rasa" (or "blank slate") and that people are born without innate ideas.
Along with Thomas Hobbes and Jean-Jacques Rousseau, he was also one of theoriginators of Contractarianism (or Social Contract Theory), which formed the theoretical groundwork of democracy, republicanism and modern Liberalism andLibertarianism. He is sometimes referred to as the "Philosopher of Freedom", and his political views influenced both the American and French Revolutions.

Life

Locke was born on 29 August 1632 in the small rural village of Wrington, Somerset, England. His father, also named John Locke, was a country lawyer and clerk to the Justices of the Peace in nearby town of Chew Magna, and had served as acaptain of cavalry for the Parliamentarian forces during the early part of the English Civil War. His mother, Agnes Keene, was a tanner's daughter and reputed to be very beautiful. Both parents were Puritans, and the family moved soon after Locke's birth to the small market town of Pensford, near Bristol.
In 1647, Locke was sent to the prestigious Westminster School in London (sponsored by the local MP Alexander Popham) as a King's Scholar. After completing his studies there, he was admitted to Christ Church, Oxford. Although a capable student, Locke was irritated by the largely classical (Aristotelian) undergraduate curriculum of the time, and found more interest in the works of modern philosophers such as René Descartes, and the more experimental philosophy being pursued at other universities and within the embryonic Royal Society.
Locke was awarded a bachelor's degree in 1656, and a master's degree in 1658. He was elected lecturer in Greek in 1660 and then in Rhetoric in 1663, but he declined the offer of a permanent academic position in order to avoid committing himself to a religious order. During his time at Oxford, he also studied medicine extensively, and worked with such noted scientists and thinkers as Robert Boyle, Thomas Willis, Robert Hooke and his friend from Westminster School, Richard Lower. He later obtained a bachelor of medicine qualification in 1674.
It was through his medical knowledge that he obtained the patronage of the controversial political figure, Lord Anthony Ashley Cooper (the 1st Earl of Shaftesbury), and in 1667 he moved to Shaftesbury's London home to serve as his personal physician. He was credited with saving Shaftesbury's life afer a liver infection became life-threatening. In London, Locke continued his medical studies under the tutelage of Thomas Sydenham, who also had a major influence on Locke's natural philosophical thinking.
During the 1670s, Locke served as Secretary of the Board of Trade and Plantations and Secretary to the Lords and Proprietors of the Carolinas, helping to shape his ideas on international trade and economics. Locke became more involved in politics (and further developed his political ideas) when Shaftesbury, a founder of the Whig movement in British politics, became Lord Chancellor in 1672. It was also during this time in London that he worked on early drafts of his "An Essay Concerning Human Understanding", eventually published in 1690 and considered one of the principal sources of Empiricismin modern philosophy.
After some time travelling across France following Shaftesbury's fall from favour in 1675, he returned to England in 1679 (when Shaftesbury's political fortunes took a brief positive turn), and began the composition of his famous work of Political Philosophy, the "Two Treatises of Government", which was published anonymously (in order to avoid controversy) in 1689, and whose ideas about natural rights and government were quite revolutionary for that period in English history.
In 1683, Locke fled to Holland, under strong (but probably unfounded) suspicion of involvement in the Rye House Plot. He did not return to England until 1688's Glorious Revolution and the overthrow of King James II by the of the Dutchman William of Orange (King William III of England), which Locke saw as the ultimate triumph of his revolutionary cause. The publication of"An Essay Concerning Human Understanding", the "Two Treatises of Civil Government" and "A Letter Concerning Toleration" all occurred in quick succession upon his return from exile. His "Essay" in particular brought great fame, and Locke spent much of the rest of his life responding to admirers and critics by making revisions in later editions of the book.
In 1691, he moved to his close friend Lady Masham's country house at Oates, Essex. During this period, he became something of an intellectual hero of the Whigs, and he discussed matters with such figures as John Dryden and Sir Isaac Newton. He continued to work at the Board of Trade from 1696 until his retirement in 1700.
However, his health deteriorated, marked by regular asthma attacks, and he died on 28 October 1704, and was buried in the churchyard of High Laver. He never married, and had no children.

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Locke wrote on philosophical, scientific and political matters throughout his life, in a voluminous correspondence and ample journals, but the public works for which he is best known were published in a single, sudden burst in 1689 - 1690.
The fundamental principles of Locke's Epistemology are presented in his monumental "An Essay Concerning Human Understanding" of 1690, the culmination of twenty years of reflection on the origins of human knowledge. In it he argued theempiricist approach that would be adopted by the British Empiricism movement: that all of our ideas, whether simple or complex, are ultimately derived from experience and sensory input. The knowledge of which we are capable is therefore severely limited in its scope and certainty, in that we can never know the inner nature of the things around us, only their behaviour and the way in which they affect us and other things (a kind of modified Skepticism). One of the ways in which they affect us is through our senses, giving us experiences (or representations or images) of their properties or qualities.
Locke saw the properties of things as being of two distinct kinds. Their real inner natures derive from the primary qualities, which we can never experience and so never know. Our knowledge of material substances, therefore, depends heavily on theirsecondary qualities (by reference to which we also name them), which are mind-dependent and of a sensory or qualitative nature. He therefore believed in a type of Representationalism, that these primary qualities are "explanatorily basic" in that they can be referred to as the explanation for other qualities or phenomena without requiring explanation themselves, and that these qualities are distinct in that our sensory experience of them resembles them in reality.
He claimed that "the mind is furnished with ideas by experience alone" (an idea being something within the mind thatrepresents things outside the mind). However, he also argued that a proper application of our cognitive capacities is enoughto guide our action in the practical conduct of life, and that it is in the process of reasoning that the mind confronts the raw ideas it has received (an approach not dissimilar to the Dualism of Descartes). His definition of knowledge might be stated, then, as the perception of the relationship between ideas.
Where Locke differed markedly from Descartes and other predecessors, though, was in the status he granted to the senses.Descartes held that the senses incline us to have certain beliefs, but that this alone does not amount to actual knowledge(which requires interpretation and explanation by reason and the intellect). For Locke, however, the senses themselves are a basic and fundamental faculty which deliver knowledge in their own right. Indeed, his whole conception of an idea differed from that of Descartes: for Descartes, an idea was fundamentally intellectual; for Locke it was fundamentally sensory, and all thought involved images of a sensory nature.
In later editions of the treatise, he also included detailed accounts of human volition and moral freedom, the personal identity on which our responsibility as moral agents depends, and the dangers of religious enthusiasm.
With his "Two Treatises of Civil Government", published anonymously in 1690 in order to avoid controversy, Locke established himself as a political theorist of the highest order. The "First Treatise" was intended merely to refute Sir Robert Filmer's support of the Divine Right of Kings, arguing that neither scripture nor reason supports Filmer's contentions. The "Second Treatise", however, offered a systematic account of the foundations of political obligation. In Locke's view, all rights begin in the individual property interest created by an investment of labour. The social structure (or "commonwealth") depends for its formation and maintenance on the express consent of those governed by its political powers (the so-called Social Contractor Contractarianism). He believed that majority rule thus becomes the cornerstone of all political order, although dissatisfied citizens reserve a lasting right to revolution.
Like Thomas Hobbes before him, Locke started from a belief that humans have absolute natural rights, in the sense ofuniversal rights that are inherent in the nature of Ethics, and not contingent on human actions or beliefs (a kind ofDeontology). However, much of his political work is characterized by his opposition to authoritarianism, and particularly to the tendency towards Totalitarianism advocated by Hobbes. Locke believed that no one should be allowed absolute power, and introduced the idea of the separation of powers, whereby the Church and the judicial system operate independently of the ruling class. In particular, he defined our civil interests (those which the State can and should legitimately protect) as life,liberty, health and property, specifically excluding religious concerns, which he saw as outside the legitimate concern ofcivil government. If much of this seems familiar from the American Declaration of Independence, that is no coincidence as the American founding fathers freely admitted their debt to Locke's Political Philosophy.
His "Letter Concerning Toleration" of 1689 came in the wake of King Louis XIV of France's revocation of the Edict of Nantes(and the religious persecution which followed it). It argued for a broad (though not limitless) acceptance of alternative religious convictions, as well as a strict separation betwen Church and State. In his 1695 "The Reasonableness of Christianity", he argued that the basic doctrines of Christianity are relatively few and entirely compatible with reason.
In 1693, Locke produced his contribution to the Philosophy of Education, his influential "Some Thoughts Concerning Education". In it, he claimed (influenced by Avicenna and the Medieval Avicennist movement) that a child's mind is a tabula rasa (or blank slate) and does not contain any innate ideas, nor anything that might be described as human nature. Thus, all men are created equal, and each of us can be said to be the author of our own character. These ideas flowed logically and seamlessly from Locke's underlying belief in Empiricism, that all human knowledge derives from the senses and that therefore there can be no knowledge that precedes observation.

According to Locke, the mind was to be educated by a three-pronged approach: the development of a healthy body; the formation of a virtuous character; and the choice of an appropriate academic curriculum. He maintained that a person is to a large extent a product of his education, and also pointed out that knowledge and attitudes acquired in a child's early formative years are disproportionately influential and have important and lasting consequences

By Historical Period > Modern > Age of Reason

The Age of Reason period of the Modern era of philosophy is generally regarded as the start of modern philosophy, and roughly equates to the 17th Century.

It includes the following major philosophers:

Hobbes, Thomas (1588 - 1679) English
Descartes, René (1596 - 1650) French
Pascal, Blaise (1623 - 1662) French
Spinoza, Baruch (Benedict) (1623 - 1677) Dutch-Jewish

Locke, John (1632 - 1704) English
Malebranche, Nicolas (1638 - 1715) French
Leibniz, Gottfried Wilhelm (1646 - 1716) German

The Age of Reason saw a continuation of the move away from theology and faith-based arguments, and marks the shaking off of medieval approaches to philosophy such as Scholasticism, in preference for more unified philosophical systems likeRationalism and British Empiricism. The advances in science, the growth of religious tolerance and the rise of philosophical liberalism also led to a revival in Political Philosophy in general.

Along with the Age of Enlightenment of the 18th Century, which the Age of Reason gave rise to, it is also know as the Early Modern period.

The Age of Enlightenment period of the Modern era of philosophy corresponds roughly to the 18th Century.
It includes the following major philosophers:

Berkeley, Bishop George (1685 - 1753) Irish
Voltaire (François Marie Arouet) (1694 - 1778) French
Hume, David (1711 - 1776) Scottish
Rousseau, Jean-Jacques (1712 - 1778) Swiss-French

Smith, Adam (1723 - 1790) Scottish
Kant, Immanuel (1724 - 1804) German
Burke, Edmund (1729 - 1797) Irish

In general terms, the Enlightenment was an intellectual movement, developed mainly in France, Britain and Germany, which advocated freedom, democracy and reason as the primary values of society. It started from the standpoint that men's minds should be freed from ignorance, from superstition and from the arbitrary powers of the State, in order to allow mankind to achieve progress and perfection. The period was marked by a further decline in the influence of the church, governmental consolidation and greater rights for the common people. Politically, it was a time of revolutions and turmoil and of the overturning of established traditions.
The major philosophical movements of the period include British Empiricism, Rationalism and Kantianism. It also saw an increasing focus on Political Philosophy.
It was essentially a continuation of the process of rationalization begun in the Age of Reason of the 17th Century, but also to some extent a reaction against it, and the two periods are often combined as the Early Modern period.

British Empiricism is a practical philosophical movement which grew up, largely in Britain, during the Age of Reason and Age of Enlightenment of the 17th and 18th Century. The major figures in the movement were John Locke, George Berkeley and David Hume.
Empiricism is the idea that the origin of all knowledge is sense experience. It emphasizes the role of experience andevidence, especially sensory perception, in the formation of ideas, while discounting the notion of innate ideas, and argues that the only knowledge humans can have is a posteriori (i.e. based on experience). It relies on induction or inductive reasoning (making generalizations based on individual instances) in order to build a more complex body of knowledge from these direct observations. Modern science, and the scientific method, is considered to be methodologically empirical in nature, relying as it does on an inductive methodology for scientific inquiry. See the section on the doctrine of Empiricism for more details.
Empiricism is usually contrasted with Rationalism (which holds that the mind may apprehend some truths directly, without requiring the medium of the senses), which became established in Continental Europe at around the same time, with the work of Descartes, Leibniz and Spinoza, among others. Locke, Berkeley and Hume vigorously defended Empiricism against theseRationalists.
The concept of a "tabula rasa" (or "clean slate") had been developed as early as the 11th Century by the Persian philosopherAvicenna, who further argued that knowledge is attained through empirical familiarity with objects in this world, from which one abstracts universal concepts, which can then be further developed through a syllogistic method of reasoning. Sir Francis Baconcan be considered an early British Empiricist, through his popularization of an inductive methodology for scientific inquiry, which has since become known as the scientific method.
However, the first explicit formulation of Empiricism was by the British philosopher John Locke in the late 17th Century. Lockeargued in his "An Essay Concerning Human Understanding" of 1690 that the mind is a tabula rasa on which experiences leave their marks, and therefore denied that humans have innate ideas or that anything is knowable without reference to experience. However, he also held that some knowledge (e.g. knowledge of God's existence) could be arrived at throughintuition and reasoning alone.
The Irish philosopher Bishop George Berkeley, concerned that Locke's view opened a door that could lead to eventual Atheism, put forth in his "Treatise Concerning the Principles of Human Knowledge" of 1710 a different, very extreme form of Empiricism in which things only exist either as a result of their being perceived, or by virtue of the fact that they are an entity doing the perceiving. He argued that the continued existence of things results from the perception of God, regardless of whether there are humans around or not, and any order humans may see in nature is effectively just the handwriting of God.
The Scottish philosopher David Hume argued that all of human knowledge can be divided into two categories: relations of ideas (e.g. propositions involving some contingent observation of the world, such as "the sun rises in the East") and matters of fact (e.g. mathematical and logical propositions), and that ideas are derived from our "impressions" or sensations. In the face of this, he argued that even the most basic beliefs about the natural world, or even in the existence of the self, cannot be conclusively established by reason, but we accept them anyway because of their basis in instinct and custom. Hume's Empiricism therefore verges on Skepticism. John Stuart Mill took this reasoning a step further in the mid-19th Century in maintaining that inductive reasoning is necessary for all meaningful knowledge (including mathematics), and that matter is merely the "permanent possibility of sensation", as he put it.
In the late 19th Century and early 20th Century, developments stemming from

By Individual Philosopher > John Locke Descartes

René Descartes
(Portrait by Frans Hals, 1649)

Introduction

René Descartes (1596 - 1650) was a French philosopher, mathematician, scientist and writer of the Age of Reason. He has been called the "Father of Modern Philosophy", and much of subsequent Western philosophy can be seen as aresponse to his writings. He is responsible for one of the best-known quotations in philosophy: "Cogito, ergo sum" ("I think, therefore I am").
He was a pioneer and major figure in 17th Century Continental Rationalism (often known as Cartesianism) later advocated by Baruch Spinoza and Gottfried Leibniz, and opposed by the British Empiricist school of thought of Hobbes, Locke, Berkeley andHume. He represents a major break with the Aristotelianism and Scholasticism of theMedieval period.
His contribution to mathematics was also of the first order, as the inventor of theCartesian coordinate system and the founder of analytic geometry, crucial to the invention of calculus and mathematical analysis. He was also one of the key figures in the scientific revolution of the 16th and 17th Centuries.

Life

Descartes (pronounced day-CART) was born in the town of La Haye en Touraine(since renamed Descartes) in the Loire Valley in central France on 31 March 1596. His father, Joachim Descartes, was a busy lawyer and magistrate in the High Court of Justice, and his mother, Jeanne (née Brochard), died of tuberculosis when René was just one year old. René and his brother and sister, Pierre and Jeanne, were therefore mainly raised by their grandmother.
From 1604 until 1612, he attended the Jesuit Collège Royal Henry-Le-Grand at La Flèche, Anjou, studying classics, logic and traditional Aristotelianism philosophy. His health was poor and he was granted permission to remain in bed until 11 o'clock in the morning, a custom he maintained for the rest of his life. He then spent some time in Paris studying mathematics, before studing law at the University of Poitiers, in accordance with his father's wishes that he should become a lawyer, obtaining hislaw degree in 1616.
However, he then abandoned his education and spent several years travelling and experiencing the world (he later claimed that his formal education provided little of substance). It was during this time (in 1618) that he met the Dutch philosopher and scientist Isaac Beeckman (1588 - 1637) while walking through Breda in Holland, who sparked his interest in mathematics and the new physics.
In 1622, he returned to France, and soon afterwards sold all his property at La Haye, investing the proceeds in bonds which provided him with a comfortable income for the rest of his life. He returned to settle in Holland in 1628. The next year, he joined the University of Franeker; the year after that, Leiden University; and, in 1635, he is recorded as attending Utrecht University. He had a daughter, Francine, after a relationship in Amsterdam with a servant girl, Helène Jans, although Francine died at the age of fve. In fact, in the years between 1828 and 1649, he lived at 14 separate addresses in 10 different Dutch cities.
It was during this 20 year period of frequent moves that he wrote almost all of his major works on philosophy, mathematics and science. He shrewdly held off publication of his first work, "Le Monde" ("The World"), written between 1629 and 1633, due to the condemnation of the works of Galileo Galilei (1564 - 1642) and Nicolaus Copernicus (1473 - 1543) by the Roman Catholic Church in 1633. The most famous of his works include: the "Discours de la méthode pour bien conduire sa Raison et chercher la Vérité dans les Sciences" ("Discourse on the Method") of 1637, his first rationalist vision of the progress of human knowledge; the "Meditationes de Prima Philosophia" ("Meditations on First Philosophy") of 1641, a more formal exposition of his central tenets, in Latin; and the "Principia Philosophiae" ("Principles of Philosophy") of 1644, an even more systematic and comprehensive exposition of his views. For a time, in 1643, Cartesian philosophy was condemned by the University of Utrecht.
Descartes died of pneumonia on 11 February 1650 in Stockholm, Sweden, where he had been invited as a teacher for Queen Christina of Sweden. Later, his remains were taken to France and buried in the church of Sainte-Geneviève-du-Mont in Paris, and then, during the French Revolution, disinterred for burial in the Panthéon among the other great thinkers of France. Currently, his tomb is in the church of Saint-Germain-des-Prés in Paris, and his brain is in the Musée de l'Homme.

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Descartes lived during a very skeptical period, at a time before science as we know it existed, and after a long period of relativestagnation in philosophical thought during the Church-dominated and Aristotle-influenced late Middle Ages. He had been impressed, in both his academic work and in his experience of the world at large, by the realization that there appeared to be nocertain way of acquiring knowledge, and he saw his main task as the epistemological one of establishing what might becertain knowledge as a stepping stone towards the ultimate pursuit of truth. His more immediate aim in this was to putscientific enquiry in a position where it was no longer subject to attack by Skeptics, and he tried to do this by a kind of pre-emptive Skepticism, essentially by being more skeptical than the Skeptics.
At the heart of Descartes' philosophical method was his refusal to accept the authority of previous philosophers, and even of the evidence of his own senses, and to trust only that which was clearly and distinctly seen to be beyond any doubt (a process often referred to as methodological skepticism or Cartesian doubt or hyperbolic doubt). Only then did he allow himself toreconstruct knowledge (piece by piece, such that at no stage was the possibility of doubt allowed to creep back in) in order to acquire a firm foundation for genuine knowledge and to dispel any Skepticism.
He outlined four main rules for himself in his thinking:

Never accept anything except clear and distinct ideas.
Divide each problem into as many parts are needed to solve it.
Order your thoughts from the simple to the complex.
Always check thoroughly for oversights.

Using this process, which he detailed in his epochal "Discourse on the Method" of 1637 and expanded in the "Meditations on First Philosophy" of 1641, Descartes attempted to narrow down, by what is sometimes called the method of doubt, what wascertain and what contained even a shadow of a doubt. For example, he realized that he could doubt even something as apparently fundamental as whether he had a body (it could be that he was just dreaming of it or that it was an illusion created by an evil demon), but he could not, under any circumstances, doubt whether he had a mind or that he could think. He followed this up with a pure, abstract thought experiment. He imagined an evil spirit (or "deceiving demon") whose sole intention was to mislead him, and asked whether there was anything about which the demon would not be able to mislead him. His conclusion was the act of thinking, that the demon could never make him believe that he was thinking when he was not (because, after all, even a false thought is still a thought).
Having identified this single indubitable principle, that thought exists, he then argued that, if someone was wonderingwhether or not he existed, then the very act of thinking was, in and of itself, proof that he did in fact exist: the famous "Je pense, donc je suis" ("I think, therefore I am") - the similar statement in Latin, "Cogito ergo sum" is found in his later "Principles of Philosophy". It is worth mentioning here that, by "thinking", Descartes did not just mean conceptual thought, but all forms ofconsciousness, experience, feelings, etc.
Having dispelled all doubt by this process, Descartes then worked to build up, or reconstitute, the world again. But he was careful not to do this willy-nilly, but only according to his own very strict rules, so that the "reconstituted world" was not the same as the original one which he had dismantled piece by piece due to doubts. The way he achieved this (which, it must be said, appears from a modern viewpoint like something of a conjuring trick) was to argue that among the contents of our (certain) consciousness was the idea of God, which in itself he saw as proof of the existence of God. He then argued that, if we have theoverwhelming impression of the existence of a concrete world around us, as we do, then an omnipotent, omniscient and omnibenevolent God would ensure that such a world does in fact exist for us. Furthermore, he asserted that the essence of this physical world was extension (that it takes up space), contrary to the extensionless world of the mind.
Paradoxically, this was an essential step forward in 17th Century science as it established a physical world which was of amathematical character and permitted mathematical physics to be used to explain it. Also important is that, as we have seen, although God was indispensible to Descartes' method of arriving at a physical world, once such a world was accepted, it was no longer necessary to involve God in the description and measurement and explanation of how things work. Thus, the process of science was freed from theological contraints and interference.
Descartes dismissed the senses and perception as unreliable, and to demonstrate this he used the so-called Wax Argument. This revolves around the idea that a wax object, which has certain properties of size, colour, smell, temperature, etc, appears to change almost all of these properties when it is melted, to the extent that it appears to our senses to be acompletely different thing. However, we know that it is in fact still the same piece of wax. Descartes concluded from this that the senses can be misleading and that reason and deduction is the only reliable method of attaining knowledge, which is the essence of Rationalism.
Descartes further argued that sensory perceptions come to him involuntarily (not willed by him), and are therefore external to his senses and therefore evidence of the existence of an external world outside of his mind. He argued that the things in the external world are material because God would not deceive him as to the ideas that are being transmitted, and has given him the propensity to believe that such ideas are caused by material things. Because of this belief that God is benevolent and does not desire to deceive him, he can therefore have some faith in the account of reality his senses provide him.
Descartes believed that the human body works like a machine, that it has the material properties of extension and motion, and that it follows the laws of physics. The pieces of the human machine, he argued, are like clockwork mechanisms, and that the machine could be understood by taking its pieces apart, studying them, and then putting them back together to see the larger picture (an idea referred to as Reductionism). The mind or soul, on the other hand, is a non-material entity that lacksextension and motion, and does not follow the laws of physics.
Descartes was the first to formulate the mind-body problem in the form in which it exists today (see the section on Philosophy of Mind), and the first to clearly identify the mind with consciousness and self-awareness, and to distinguish this from the brain, which was the physical seat of intelligence (Dualism). In his epistemological work in the "Discourse on the Method", he had realized that, although he could doubt that he possessed a body, he could not under any circumstances doubt that he possessed a mind, which led him to conclude that the mind and the body were two very different and separate things. His particular form of Dualism (known as Cartesian Dualism) proposed that the mind controls the body, but that the body also influences the otherwise rational mind (such as when people act out of passion) in a kind of two-way interaction, which he claimed, without much evidence, occurred in the pineal gland. Gilbert Ryle later described this kind of Dualism (where mental activity carries on in parallel to physical action, but where their means of interaction are unknown or, at best, speculative) as the "ghost in the machine". Although his own solution was far from convincing, this kind of Cartesian Dualism set the agenda for philosophical discussion of the mind-body problem for many years after Descartes' death.
It should be noted, however, that for all Descartes' innovation and boldness, he does not abandon the traditional idea of God. He defined "substance" (essentially meaning what the world really consists of) as "that which requires nothing other than itself in order to exist", but he concluded that the only true substance was God himself, because everything else (from souls to material objects like the human body) was dependent on God for its existence. He used his own variations of the causal argument, theontological argument and the cosmological argument for the existence of God in his "Meditations" (see the section onPhilosophy of Religion), and the existence of God played a major role in his validation of reason and in other parts of Descartes’ system. Given the important rôle God plays in his work, suggestions that Descartes was really a closet atheist, and that he includes the arguments for the existence of God as window dressing, appear extremely unlikley.
In mathematics, Descartes realized that a graph could be drawn to show a geometrical interpretation of a mathematical function using points known as Cartesian coordinates, and thereby founded analytic geometry or Cartesian geometry(using algebra to describe geometry), which was crucial to the subsequent development of calculus by Sir Isaac Newton (1643 - 1727) and Gottfried Leibniz. He also invented the notation which uses superscripts to indicate powers or exponents, and hisrule of signs is also a commonly used method to determine the number of positive and negative zeros of a polynomial. It can be argued that his reflections on mind and mechanism, impelled by the invention of the electronic computer and by the possibility of machine intelligence, blossomed into the Turing test of a machine's capability to demonstrate intelligence.
In optics, he showed by using geometric construction and the law of refraction (also known as Descartes' law) that the angular radius of a rainbow is 42 degrees. He also independently discovered the law of reflection (that the angle of incidence equals the angle of reflection).
In physics, Descartes introduced (before Newton) the concept of momentum of a moving body (what he termed the "amount of motion"), which he defined as the product of the mass of the body and its velocity or speed. His three "laws of nature" became the basis of Newton's later laws of motion and the modern theory of dynamics: that each thing tries to remain in the same state and, once moved, continues to move; that all movement is along straight lines; and that when a body comes into contact with another body the combined "quantity of motion" remain the same (his conservation of motion principle).

In an attempt to explain the orbits of planets, Descartes also constructed his vortex theory which would become the most popular theory of planetary motion of the late 17th Century (although subsequently discredited). However, he continued to cling to the traditional mechanical philosophy of the 17th Century, which held that everything physical in the universe to be made of tiny "corpuscles" of matter (although, unlike Atomism, the theory maintained that there could be no vacuum, just a mass of swirling matter).

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