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In medieval times philosophy took up a new role. The Greeks had lived before Christ and well before Christianity became an established religion. The most famous philosophers of the medieval period were Christians. Their belief in the existence of God was firm and unshakeable. Yet they wished to make clear the exact nature of their belief, and to see if it could be proved by a valid argument. Thus they were philosophers as well as Christians; but with them reasoning would not be allowed to overcome faith.
St Anselm (1033-1109) was archbishop of Canterbury. In his book, the Proslogion, he was the first to put forward a famous argument for the existence of God, known as the ontological argument. This argument runs roughly as follows: God is the greatest possible being - it is part of the very idea of God that He is such a being. Now, the greatest possible being must exist. So God, the greatest possible being, must exist. Some later philosophers accepted the argument, but others rejected it. St Thomas Aquinas (1226-74) Put forward his own 'five ways' of proving the existence of God in his long book Summa Theologica. These all argue that there must be a God, starting from various facts about the nature of the world around us. Since they were put forward, these arguments have been much discussed and disputed.
Modern philosophy is often held to have begun in France with Rene Descartes (1596-1650). Descartes certainly saw himself as breaking away from all the earlier philosophical 'schools', and starting out on his own in a completely new way. In his Discourse on Method Descartes set out his method of reaching truth in all matters. In the Meditations Descartes tells us about the results he came to using this method. He began by asking which of his present beliefs could not possibly be false. Surely his belief that he was now sitting at his desk must be a true belief? But, he remembered, he had often dreamed that he was sitting up at his desk, when in fact he was really asleep in bed. So he might be wrong -he might be dreaming now.
Descartes concluded that the one belief he could not doubt was that he was thinking. He could be sure that he thought he saw a desk, even if he couldn't be sure that there was a desk in front of him. So Descartes found the first premise of his philosophy: I think. Further, if he could not doubt that he thought certain things, he certainly could not doubt that he existed. He is therefore quite certain of his own existence - at least insofar as he is a thinking being. 'I think, therefore I exist: cogito, ergo sum.'
Descartes was convinced that his mind and his body were two quite different things. He argued that whereas it was possible to doubt that his body really existed, he could not doubt that his thinking mind existed. So mind and body were distinct things. This view is known as mind-body dualism. One of the problems Descartes left with later philosophers was this: how is the mind of a man connected to his body? This became known as the mind-body problem.
(1646-1716) German philospher and mathematician. He is ranked with Newton as one of the two great intellects of the 17th century. There is some dispute whether he or Newton first discovered the in'initesimal calculus. His best-known work is Monadology and he left a vast correspondence with learned men of his day which expresses his views.
Descartes, and those who followed him in the use of the 'mathematical' method in philosophy, have been called rationalists (from the Latin ratio meaning reason). Rationalist philosophers think that we can find out what the world contains by careful reasoning from obviously true premises; these premises can be known to be true without our needing to observe or experiment on the world around us. They sometimes call these premises innate truths - meaning that we are born (Latin nati) already knowing their truth.
Baruch Spinoza (1632-77), a Dutch lens-grinder, and the Prussian, Gottfried Leibniz (1646-1716), are two famous rationalists. In his main work, the Ethics, Spinoza tried to develop and improve upon Rene Descartes's philosophy.
Spinoza saw man as merely a part of nature; further, all events are connected and influence one another. An adult man's character is the result of the way other things and people acted upon him when he was a child. So, Spinoza concludes, we should not behave as if people could ever have acted otherwise than they did. We should not show anger or resentment, but only calm understanding, in the face of another person's stupid or wicked actions.
The view that all of a man's future actions are fixed in advance, or predetermined, is known as determinism. Philosophers today still discuss the view that we cannot hold a man responsible for his actions if they are all determined.
Leibniz, a brilliant mathematician as well as a philosopher, wrote out his main ideas in his Monadology; this title means 'theory of monads'. Monads are simple, mind-like substances of which, according to Leibniz, the world is made up. Leibniz tried to prove that the world must be made up of innumerable monads and that all that really exists are these monads. If his conclusions do not appear to be true according to our observations of the world, he would answer, like Parmenides, that our observations of the world do not inform us about what the world really contains.
Faced with conflicting views of what there is, we may begin to wonder how we are to decide between them. One way of telling if a statement is true or false is to look and see. If I say, 'There's a cat on the mat', and you see nothing on the mat, you will conclude that what I said was false. In this way we frequently use the evidence of our senses to tell if a particular claim about the world is true. A group of philosophers who claim that our only way of telling what there is, is by using the evidence of our senses, are the empiricists (from the Greek word for experience). A claim which cannot be tested by our senses can be ignored, they say: it can give us no knowledge of the world about us.
The first modern empiricists were John Locke (1632-1704), George Berkeley (1685-1753) and David Hume (1711-76).
In his Essay Concerning Human Understanding Locke attacked the rationalist view that there are some beliefs which are innate, or inborn, in the human mind. Locke claimed that, on the contrary, the minds of children at birth are like blank sheets of paper. The rationalist thinkers, Locke argued, had no right to expect us to believe certain premises because according to them they were innate. There are no innate beliefs.
Locke's own picture of the world was taken over from the scientists of his day, Boyle and Newton. Objects in space close to our bodies cause sensations (called by Locke 'ideas') to occur in our minds. When we have these sensations we say that we perceive (see, hear, feel, touch or smell) the objects themselves. Locke's theory suggests the question: 'How do we know that objects in space are in any way like the sensations they produce in our minds?'
Berkeley tried to answer this question in his Principles of Human Knowledge. He said that we cannot even know that objects outside our minds cause sensations. All we are ever conscious of are the sensations themselves, so our knowledge is limited to knowledge of our own sensations. For how can we have any grounds for our beliefs, if they are about anything but our sensations?
David Hume, who gave his ideas of the limits of knowledge in his Treatise and Enquiry, doubted the existence of all things apart from his own sensations and thoughts. He said that he had no idea what the human mind could be apart from a 'bundle' of experiences. His own experiences were all he knew about for certain.
Immanuel Kant (1724-1804), the great German philosopher, felt challenged by Hume's scepticism, and began to think carefully for himself about the nature of human knowledge. He wanted to know what kinds of things we could know, and what kinds of things, if any, we could never know. His book, The Critique of Pure Reason, is perhaps the greatest masterpiece of philosophy. As Kant himself was aware, it is difficult to understand. But it is worth the trouble of trying to do so.
Kant is not sceptical, in Hume's way, about the existence of material objects in space. He argues that we must believe that there are enduring things around us in space, or how could we connect together our different sensations, and how remember them? Kant claimed that we needed to think of our experiences in terms of objects, if we were to have any grasp of our experiences at all.
Kant also wrote important books on ethics (the Critique of Practical Reason) and aesthetics (the Critique of Judgement). In answer to Socrates's question, 'How ought one to live?' he wrote that we act well only when we act as we would wish all men to act in our situation.
Two other philosophers who gave a famous answer to Socrates's question are Jeremy Bentham (1748-1832) and John Stuart Mill (1806-73). They developed the theory known as utilitarianism. According to this theory, one should act in such a way that one produces the greatest possible pleasure or happiness by one's action. The moral rule laid down here is sometimes called 'the Greatest Happiness Principle'. There have been many objections to this principle. One was this: if I have promised to pay you a sum of money tomorrow, then I ought to pay you that money, even if, by giving it to a beggar instead, I could produce more happiness than by giving it to you.
Political philosophy has not been neglected by modern philosophers. Thomas Hobbes (1588-1679) took up the sophists' question, 'Why should we obey the laws of our country?' in his great book Leviathan. He argued that men could only live happy lives if they lived in a society with one firmly established ruling body or sovereign which made laws for everyone. If men lived without a sovereign and without laws, their lives would be 'nasty, brutish and short'. In such a state of nature, as he calls it, each man would be at war with every other man. So, for their own good, all men should agree to abide by the laws of one sovereign. Having once handed over the right of law-making to the sovereign, men are duty bound to obey him and all his laws.. These laws impose many further duties on the citizens, such as the duty not to kill other citizens.
John Locke, the empiricist, also wrote on political philosophy. His most famous work in this field is the Two Treatises on Government. He emphasised that the role of laws is to hedge us in from 'bogs and precipices'. Laws do not only provide us with duties, but also with rights. If other men have the duty not to kill me, then I have the right to live. Locke believed that everyone living in a society has a duty to obey the laws of that society, provided that these laws actually protect the interests of society. He claimed that merely by continuing to live in a certain country one had given tacit (silent) consent to the laws of the government in power.
Jean-Jacques Rousseau (1712-78) also made use of the notion of consent or agreement in discussing whether or why we have a duty to obey the laws of our country. In The Social Contract he describes what for him would be an ideal type of society. This is one in which all the citizens together agree upon each law that is made. Rousseau felt very strongly that only such a process of agreement between citizens can create a citizen's duty to obey the laws.
In the years following the publication of Kant's great works, philosophy nourished in Germany. The most outstanding and influential philosopher was Friedrich Hegel (1770-1831). Hegel's thought covered all the branches of philosophy. He saw philosophy as a study demanding great learning and skill. He himself tried to present a view of the nature of the whole universe, not only as it is now, but as it has been and as it will be.
Hegel has been called an idealist since he claimed that the most important factor in the world was consciousness and knowledge. Sometimes he writes as if individual men's minds are part of one great spirit (the Absolute) which guides the course of the world. But human progress in knowledge was of great importance, and philosophy was the most important study of all. For philosophy had to consider the whole range of human knowledge - history, politics, art, science, religion - and discover how the different parts are connected. The business of the philosopher is to see the world as a whole, and to know how parts are related to one another. When human knowledge of the world is complete the world will have reached its state of perfection.
Hegel had many followers, including F. H. Bradley (1846-1924) in England. There were also anti-Hegelians, but, like Hegel, they often chose to describe the world as a whole, to give a 'total vision' of the world. Arthur Schopenhauer (1788-1860) disagreed with several of Hegel's basic ideas. His best-known work is The World as Will and Idea. Each of us knows what it is to exercise our will - to act with purpose, to decide we want something and to go out and get it. We ourselves have our own wills and we also have 'ideas' (sensations). We do not produce our ideas and what does, Schopenhauer says, is an unseen will which underlies the universe. Schopenhauer, unlike Hegel, did not believe in any progress towards a state of final perfection. The will, he said, cannot ever find satisfaction or be calm.
Marx and Nietzsche
A philosopher who opposed Hegel in a different way was Karl Marx (1818-1883). Marx gave up Hegel's notion of a spirit which directed natural processes. As far as Marx was concerned there was only the material world plus human minds. He called his philosophy materialism, because he rejected the Hegelian world-spirit. He saw the process of human history as a gradual progression towards the ideal state of communism, in which there would be no exploitation of one person by another. Marx disagreed with Hegel's view that it is the philosopher's job merely to understand how the world works. Understanding should lead to criticism, and criticism to revolution. And Marx's doctrines have in fact had a revolutionary effect on recent history.
Friedrich Nietzsche (1844-1900) also attacked Hegel and denied the existence of some invisible guiding will behind the scenes. He says, rather, that there is a perfectly visible will to power everywhere in the world. All men desire power. Our desire for knowledge of the world comes from our wish for power over the world. The real goal of men is to become supermen.
A Dane, Soren Kierkegaard (1813-55), another philosopher who was hostile to Hegel's views, was also the first of one of the best-known modern groups of philosophers, the existentialists. He, in fact, first used the word existentialism.
Kierkegaard wrote many books, some of them with dramatic titles like Fear and Trembling. One title, Either -Or, expresses the core of Kierkegaard's philosophy, the notion of human choice between alternative courses of action. For Kierkegaard one of the most striking features of human existence is that each individual man can choose what he wants to do and, particularly in the sphere of religion, what he wants to believe. He objected to Hegel's view of the individual as merely a part of the universe, whose goal should be to understand the whole.
The most famous existentialist, Jean-Paul Sartre, also stresses the fact that we can all choose what to do, and what to become. Someone who is a waiter today does not have to be a waiter. He could decide to give up his job. Even if he does not give up his job, he does not have to carry it out in a particular manner. Men are not like machines, which have to do one particular job in one particular way. Each man is completely free to do what he wants, Sartre says, and must realise this if he is to know the truth about himself. Sartre has expressed these views in a long philosophical work, Being and Nothingness, and also in novels and plays.
(1872-1970) English philosopher and mathematician. One of the greatest logicians of all time. Twice imprisoned for his vigorous pacifist views. Despite his position as a great English philosopher of the 20th century, it is as a figure of protest, particularly against war and the use of nuclear weapons, that he is best known.
20th Century Philosophy
Many 20th-century philosophers have tended to discuss limited problems in a detailed, careful manner. Studies in logic have developed rapidly. The work of Gottlob Frege (1848-1925) and Bertrand Russell (1872-1970) is among the best known in this field. Many logicians have also become interested in the nature of mathematics. With A. N. Whitehead (1861-1947) Russell wrote Principia Mathematica, an outstanding work in this field.
A home-grown American school of philosophy is pragmatism. The original pragmatists were C. S. Peirce (1839-1914), William James (1842-1910) and John Dewey (1859-1952). The pragmatic theory of truth says that a statement is true if it is useful for us to believe it.
One school of philosophy which became popular in Britain and America originated in Vienna, among the members of a group known as the Vienna Circle. These men were all mathematicians or scientists, and their doctrine is known as logical positivism or logical empiricism. According to their theories, only statements which can be verified (shown to be true) by our looking about us, by the evidence of our senses, can be said to tell us anything, or to be meaningful. This principle was used by members of the Circle in order to show that many of the doctrines of past philosophers had been meaningless. In Britain, A. J. Ayer's book Language, Truth and Logic brought logical positivism to people's attention. These philosophers and, later, many philosophers in Britain, were influenced by the work of an outstanding Austrian philosopher, Ludwig Wittgenstein (1889-1951). His early theories were to do with the need for a 'perfect' language which would picture facts in a clear way. He did not believe any actual human language was perfect. Later in his life Wittgenstein claimed that many philosophic problems arise because we are misled, or worried in one way or another, by our language. For instance, we might find ourselves talking about time - 'How much time has passed since I last saw you?' — and suddenly wonder, but what is time? Similarly we might feel puzzled or worried about the nature of reality -'Is it real, or am I dreaming?' These worries lead to some of the oldest and most famous questions of philosophy. Wittgenstein suggests that they should be answered by carefully considering the actual use we make of words.
Many Anglo-American philosophers have said recently that the job of philosophy is to analyse concepts, which is roughly the same as to study and explain word meanings. They would agree with Wittgenstein that philosophy 'changes nothing'. The philosopher's business is description merely.
We know that not all philosophers have held this view of their subject. Some, perhaps, would have found this view helpful and useful. But it seems a long way from the theories of Leibniz, the doubts of Descartes, the scepticism of Hume, and the answers of Kant.