Notes on Descartes and his Predecessors

In order to understand Descartes (and most other philosophers), it helps greatly to know a little about Plato and Aristotle and other major philosophical and scientific ideas that were influential before the seventeenth century.
 

Some of the summaries here are based on entries in The Oxford Companion to Philosophy, edited by Ted Honderich (Oxford University Press, 1995).

Plato

• Born circa 428 BC, died 347 BC
• He formed his ‘Academy’ in his home city, Athens.
• Athens was a great military and intellectual power, ruling over much of the area around it, including what is now known as Greece, Turkey and even parts of northern Africa.
• Athens was a democracy, (but did not give rights to women or slaves).
• He argued that our senses, (sight, touch, smell, sound), do not give us reliable knowledge. Ultimate reality is very different from how it appears to us.
• Ultimate reality is an abstract realm: the clearest example we can have of it is the world of mathematics. It contains the essences of things, which are called ‘Forms."
• Plato believed that we are already born with innate knowledge of the Forms. Learning about reality is really a matter of recalling what is already buried in one’s mind.
• Plato believed that the mind is separable from the body, and that there could be reincarnation of a person from one life to another.
• Philosophers are the people with the best knowledge of ultimate reality. They have the clearest understanding of right, wrong, and justice. Therefore he thinks that philosophers are the people who should run society.
• The rulers of society should aim to maximize the happiness of the people. The best way to do this is to impose strict censorship. He believed that the exposing people to the wrong ideas merely confuses them and leads them to interfere in what is not their business.
• Plato did not believe in individual rights to liberty or democracy.

Aristotle

• Born in northern Greece in 384 BC, his father was a doctor at the court of the King of Macedonia. He went to Athens to study at Plato’s Academy at the age of 17. He left Athens after Plato’s death, but returned about 12 years later to found his own philosophical school. He stayed for about 12 years, until he had to flee the city due to the Athenians’ strong anti-Macedonian political feelings. He died the following year, in 322 BC.
• Aristotle was a biologist as well as a philosopher. His approach to philosophy was strongly influenced by scientific method. He disagreed with Plato about many issues; a crucial difference is that he thought that we could have knowledge of ultimate reality with the help of our senses.
• Aristotle saw humans as biological organisms, and this organized both his view about our psychology and our ethics and politics. He thought that our soul is simply what organized our bodies, and that animals have souls too, although only humans have the capacity to be rational. He did not think that our souls survived our physical deaths.
• He did believe that a god exists, although god does not play any role in his view of ethics or politics.
• He thought that our well-being consists in living a good life, and we can do this by becoming virtuous. Notice this means, at least in the ideal state, that there should be no conflict between what is best for oneself and what is best for society.
• Aristotle devoted much of his ethics to discussing desire, goals, imagination, emotion, and intuitions in the choices and intentional actions of the virtuous. He was concerned to explain weak-willed action and self-control.
• Aristotle thought of humans as political animals, in the sense that they need each other for friendship and in order to display virtues like courage, generosity, and justice, which are part of a good life.
• A city-state has as its goal well-being, and the ideal constitution is one in which every citizen achieves well-being.
• In practice, democracy is preferable to oligarchy because it is more stable and its judgments are likely to be wiser since individuals when grouped together have more wisdom than a few.
• The practice of slavery, with regard to both ‘natural’ and ‘non-natural’ slaves required to till the soil and maintain the state is justified. Natural slaves are people who lack the abilities to live a life of excellence.
• Children born with serious physical handicaps should be left to die.
• Aristotle criticized Plato’s idea that philosophers should decide what is best for everyone else, on the grounds that it undermines private property and friendship, which are the greatest safeguards against revolution.

Scholasticism

This is the philosophy of the ‘schools’ associated with the methods and theses of the major philosophers of the thirteenth and fourteen centuries, namely, Thomas Aquinas (c. 1224-1274), John Duns Scotus (c. 1266-1308), and William Ockham (1285-1347).

Aquinas went to the University of Naples in his mid-teens. In 1242 he entered the Order of Preachers (the Dominican Order). In 1256 he received a license to teach from the University of Paris, and went on to teach also at Orvieto, Rome, and Naples. He was canonized in 1323.

One of his main aims was to show how the main ideas of Aristotle are compatible with Christianity. He believed that it is possible to prove through the use of reason that God exists, that he is a unity, and that he is incorporeal. He also thinks that we can achieve this knowledge through revelation.

The philosophical movement based on Aquinas’ work is called ‘Thomism.’
 

Galileo Galilei (1564-1642)

Galileo was an astronomer and physicist who supported freedom of inquiry and expression. He insisted that mathematics was at the heart of physics, and developed laws of motion by introducing careful measurements into empirical investigation. He discovered powerful evidence against the Aristotelian-Ptolomeic view of the cosmos, which saw the earth as the center of the universe, and held that there was a dramatic difference between terrestrial and celestial phenomena. Instead Galileo argued for the Copernican view of the universe which had the earth orbiting the Sun.

In 1633 Galileo was condemned by the Catholic Church for endorsing Copernicanism and possibly also his atomist theory of matter, which was seen as incompatible with the doctrine of transubstantiation. He publicly recanted by continued his scientific work in private. It is important to remember that Galileo was also a religious man: he did not think his science forced him to abandon religion.
 

René Descartes (1596-1650)

• Descartes is the main figure associated with the intellectual revolution against medieval and Renaissance scholasticism.
• He was a ‘natural philosopher;’ his work spanned both natural science and philosophy. He did work on physics and cosmology, and scientific methodology. He was not primarily concerned with ethical or social issues.
• He rejected the Aristotelian idea that there is a fundamental difference between terrestrial and celestial phenomena. He argued that all objects in the universe obey the same physical laws.
• His main aim was to show how the world of physics, the mathematically describable world, could be reliably mapped out independently of the often vague and misleading experiences from our sensory organs.
• His most famous philosophical work is the Meditations on First Philosophy (written in 1637, published in 1641). He explains how he is aiming to start the search for truth afresh, because previous attempts have run into such difficulty.
• The primary problem in the search for knowledge is that our senses give misleading impressions. There are many visual illusions, such as a stick in water looking bent when it is in fact straight.
• Descartes argues that there can be even more widespread uncertainty about what our senses tell us, on the grounds that there is no certain way to tell whether or not we are currently dreaming. This can cast into doubt even the idea that there is a physical reality external to our minds.
• In his search for certainty, Descartes uses the following method. He supposes, for the sake of his argument, that a "malicious demon of the utmost power and cunning" is trying to deceive him about everything he thinks he knows. Is there anything that he can be certain of, even if such a demon exists?
• His answer is yes: he can be certain of his own existence. "Let the demon deceive me as much as he may… I am, I exist, is certain, so long as it is put forward by me or conceived by my mind" (Second Meditation). This is expressed in the phrase "I think, therefore I am."
• Note that Descartes can not be sure of his own existence if his mind is not active: he may not exist when he is not conscious.
• Descartes goes on in the Meditations to give an (attempted) proof of God’s existence. Once he believes that he has proved God’s existence, he thinks that he can assume that God is good, and that he is one of God’s creatures, so that when some idea appears to him to be absolutely certain (what he terms "clear and distinct,") it follows that it must be true. God is not a deceiver.
• Descartes goes on to conclude that the nature of mind (or soul) is to think and sense. It is non-physical. The mind controls the body through interaction with the brain. Note that for Descartes, the mind is NOT the same thing as the brain; in fact, it is entirely different. Our bodies are like machines that are controlled by our minds.
• Descartes held that animals are just machines, and do not have minds.

"MEDITATION I"

Descartes' philosophical project was to find a secure foundation on which to base all knowledge. The most secure form of knowledge is that which is certain. So his aim was to find certainty. In his major work, The Meditations, he goes through six stages of deep thinking, supposedly taking a day for each stage. By the end, he believes he has succeeded in his project, and that he has justified nearly all of our everyday, scientific, and religious beliefs.

However, at the start of the project, he is looking for certainty, and he does this by excluding any of his beliefs which are open to doubt. In Meditation I he goes through each sort of belief he has, and considers whether there might not be reasons to doubt them. To his alarm, he founds that nearly all can be doubted.

He starts off with knowledge that he obtained through his senses. We can divide that knowledge up into two parts, what is in our memory and what we are currently aware of. Our memory can be mistaken, so it would seem that our current experience should be more certain than memories of experiences. Descartes happened to be seated by the fire in a winter dressing gown when he was writing this Meditation, and he was aware of those things as well as his body. As I am writing this, I am aware of my cat sitting on my lap, the computer screen in front of me, the house plants to my left, and music from the radio, as well as my hands in front of me. Presumably you are aware of similar sorts of things as you read this. Isn't this kind of knowledge certain? Surely, Descartes reasons, to seriously doubt those things would be like mad people "whose brains are so disordered and clouded by dark bilious vapours" claiming that they are kings, or that messages are being beamed into their brains by the CIA.

But while he agrees with what he has just said, he nevertheless things that there is reason to doubt his senses. His argument is that he has had dreams which have felt so real that they were just as vivid as his experience when his is awake, and so he cannot be certain that he is really awake. He knows that his experience while dreaming does not correspond to reality, so if he might be dreaming, he cannot be sure that what is thinks he sees and hears is really there. With this simple argument, Descartes decides that none of that the knowledge that he gets through his senses is sufficiently certain to act as foundation for the rest of his knowledge.
 

While our experience might be just an illusion, Descartes suggests that even illusions contain some reality. Fantastic creatures in dreams still have features that are based on those of real creatures, and the colors are based on real colors. Furthermore, whether in dream or reality, we know that physical ("corporeal") objects have some size (what Descartes calls "extension"), and they can be counted (i.e., there's a certain number of them in a certain space). The doubtfulness of our senses means that we have to doubt all our scientific knowledge, but Descartes is suggesting that we might still be certain about our mathematical knowledge, such as arithmetic and geometry.

As soon as he has made this suggestion, though, he immediately retracts it. For he thinks that he has a reason to doubt even his mathematical knowledge. Maybe even the very ideas of space, numbers, shapes and size are illusions. Maybe every time he does a simple sum such as 2+3=5, he makes a mistake. We might find it hard to imagine how we could make such ridiculous mistakes, but Descartes suggests that we could be forced to make such mistakes by a very powerful God. He believes in an all powerful God, and such a being would obviously be able to fool him. Although he does not think God would fool him like that, because God is supremely good, he cannot be certain about the nature of God or what God's intentions are. Especially since he knows that God allows him to be mistaken some of the time, which is hard for him to explain.

Now Descartes has found reason to doubt everything that he had previously thought was certain. In order to avoid slipping into his old patterns of thought and unknowingly reintroducing mistakes into his reasoning, he plans to assume (for the sake of this inquiry) that everything that he has previously believed is false. He will do this by assuming that he is being deceived as much as possible by a "malignant demon."

In the second meditation, Descartes goes on to realize that even when he is doubting everything, he can still be certain of one thing, which is his own existence as a thinking being. From that discovery, he thinks that he can prove the existence of God, and from that, he finds reason to reclaim all of his former beliefs. But most philosophers today think that his proof of the existence of God does not work, and so everything that follows from it is not well supported. So his project of making all our knowledge certain is considered a failure. But it is an extremely important failure, because it suggests that maybe the whole project was wrong-headed. Maybe it is a mistake to insist on unattainable certainty. But then we need to find some reasonable alternative to certainty.