The Enlightenment

The characteristics of the Enlightenment are a scepticism towards the doctrines of the church, individualism, a belief in science and the experimental method, the use of reason, that education could be a catalyst of social change and the demand for political representation. Its main social and political consequence was the French revolution.

The core period of the Enlightenment was second half of the eighteenth century. The thinkers associated with the Enlightenment include d'Holbach (1723-89) and the Encyclopedists in France, David Hume (1711-76) in Scotland and Kant in Germany. To understand the Enlightenment we have to look at what preceded it.

The battle of ideas that was to culminate in the Enlightenment began in the seventeenth century. Francis Bacon (1561-1626) advocated the use of scientific method and René Descartes (1596-1650) proposed a critical rationalism. The Enlightenment can be understood as the culmination of the move away from the authority and dogmatism of the mediaeval and the awakening of modernity.

Medieval philosophy combined Christian beliefs with the ideas of Plato and Aristotle. In the medieval world philosophers respected their predecessors and accepted their methods. If a new discovery about nature contradicted one of Aristotle's principles, for example, it would probably have been assumed that it was the discovery that was in error.

Enlightenment thinkers were not content to accept appeals to Aristotle's authority. It could be seen that using experimental methods science was progressing and increasing our understanding of nature, which could not have been done without rejecting some of Aristotle's assumptions.

It was not only Aristotle that was being questioned, using reason and logic philosophers criticised political and religious ideas. What rational answer is there for the justification of monarchy or that you should choose one type of religion over another?


A Rationalist is a philosopher who believes that we can gain knowledge by the use of reason alone, without reference to the external world.

Rationalism has a long history in philosophy, Plato (c. 427-347 BC) was a rationalist. René Descartes (1596-1650), the "father of modern philosophy" was the first modern rationalist. He felt that philosophy should move away from the beliefs of the medieval scholastics and found itself on firm foundations. He was looking for certainty, and used his method of doubt to try and find what was indubitable.

He imagined that his whole life could be a hallucination caused by a "malicious demon". If this was the case, what could he be sure of? Descartes realised that he could not doubt that he was thinking, as doubt is a type of thought. So, without any reference to the external world Descartes was sure that he had found a basic truth that could not be questioned. Of course once he released that he was thinking he could no longer doubt that he existed (something must be doing the thinking). This enabled him to build up a philosophical system based on thought alone.

Once Descartes had reintroduced, critical questioning into philosophy the scene was set for the hundred-year struggle that was to lead to the Enlightenment.

Other rationalist philosophers include Spinoza, Leibniz, Kant and Hegel.


Empiricism is the belief that all knowledge comes from experience. The "empirical world" is the world of the senses, i.e. the world we can see, feel, touch, hear and smell.

John Locke (1632-1704) thought that the human mind at birth was a tabula rasa (blank tablet) on which experience writes the general principles and details of all knowledge. This is completely opposite to the rationalists (see above). Whereas a rationalist would attempt to find knowledge by thought alone, an empiricist would use the methods of the experimental sciences.

This emphasis on science and experiment is one of the characteristics of the Enlightenment. D'Holbach (1723-89) published his Systèm de la nature (1770) in which he asserted that explanations of nature should not be sought in traditional beliefs or the "revelations" of the church, but through the application of scientific method

It was not until Kant (See later) that empiricist and rationalist strains were bought together.

The Encyclopedists

The Encyclopédie ou Dictionnaire Raisonné des Sciences, des Arts et des Métiers was published in seventeen volumes between 1751 and 1765. Its aim was to provide information on every sphere of knowledge, and in particular to promote the application of science in industry, trade and the arts. It is seen by many as epitomising the sprit of the Enlightenment.

Denis Diderot (1713-1784) was the main editor. He was a committed empiricist and wrote on philosophy, religion, political theory and literature. He was highly critical of the church's influence on ideas.

Voltaire (pen name of François-Marie Arouet) (1694-1778) also edited and contributed to the Encyclopédie. He was anti-Christian and critical of the clergy, the king and the privileges of the nobility. He was highly influential in the rise of liberal thought in continental Europe.

Jean-Jacques Rousseau (1712-1778) wrote on music and political economy. Later he quarrelled with Diderot and came to regard the Encyclopédie as the work of the devil.

Rousseau was not alone. In 1752 and 1759 the Jesuits managed to suppress publication, although in each case for only a short period. Diderot however remained firm and by 1772 a further eleven volumes of plates were published. Diderot's ambition "to change accepted habits of thought" was in largely successful.

The analytic/synthetic distinction

Some statements we judge to be true or false in relation to facts in the world, for example that you are now reading this web page. That you are reading this web page is called by philosophers a synthetic truth.

Other statements we judge to be true due to the meanings of the words involved. We can know that the sentence "All bachelors are unmarried." is true without having to do a survey of bachelors, because the sentence is true by definition. It is an analytic truth.

Synthetic truths are "truths of fact" and analytic truths are "truths of reason". We use empirical methods to verify synthetic statements and rationalist methods to verify analytic statements.

Kant was the first to use the terms Synthetic and Analytic. He pointed out that all analytic truths are necessary, that is, they could not have been otherwise. If you agree that the definition of a bachelor is an unmarried man, then it stands to reason that all bachelors are unmarried.

Synthetic statements are not necessary. Philosophers use the word contingent to describe something that is not necessary. It is not necessarily true that you are reading this webpage: you could be reading a printout, for example.

It is important to make the analytic/synthetic distinction in argument. If you try to argue that something is true you need to be clear about whether you are saying something about the empirical world, or whether you are clarifying the meanings of words. It would do you no good for example to hunt for a bachelor who was married to try and refute the statement. It would be no help to you to try and find a "good murder" to refute the statement that all murder is bad, because murder is by definition bad.


Good philosophy must be based on good arguments, not arguments in the sense of quarrels, but reasoned arguments. Logic can be understood as the science of proper reasoning; what separates a good argument from a bad one. A useful way to understand arguments and what makes them good or bad is to divide them into two types: Deductive and inductive.

In a deductive argument, the conclusion is said to be true if it follows from the premises (starting statements). The best known form of a deductive argument is the syllogism, the simplest of which consists of two premises and a conclusion:

However if the first premise was "Some philosophers are wise" we could not be sure that Socrates was wise, as he may have been one of the philosophers who wasn't. Deductive logic does not appeal to empirical evidence, so long as the premises are true and the argument is valid then the conclusion must be true.

Inductive logic is concerned with making generalisations about the empirical world based on observation. It is closely connected with experimental science (an experiment is a particular type of observation). Let's say we were interested in the personality of people with different astrological signs and we observed that Virgo's were tidy. We may want to make a generalisation based on this. However, although our observations may back up this generalisation we cannot be sure that it applies to all Virgo's, only those we have observed. There may be Virgo's in the future, or in some other country that are not like that.


The idea of determinism is that all events are the results of previous causes. If we heated a bar of iron, and the bar expanded, we would say that the heat was the cause of expansion.

The idea of a physically determined universe is associated with Sir Isaac Newton (1642-1727). This is sometimes called the billiard ball view of nature: A billiard ball will only move when acted on by another force such as another billiard ball hitting it. If we could measure the exact velocity and angle of the first billiard ball, we could predict the movement of the second.

The philosophical problem comes with human beings. If we were to accept the empirical view that human beings are organised systems of matter and that our minds are formed as a result of experiences then we may want to explain human behaviour in terms of cause and effect.

If we knew enough about the biological make up of an individual, his early childhood experiences and the social and historical circumstances he was born into, then perhaps we could predict all of his actions. From this point of view the idea of free will (the ability to choose) is simply the result of or ignorance of all of the causal factors.

This is as much a problem for the present day as it was for the thinkers of the Enlightenment. I may think that I am in love with a unique soul mate, but it may be that my body is producing chemicals that make me fall in love in order that I reproduce the species.

If there is no such thing as free will then we cannot apply moral concepts such as good and bad. Morality can only exist were there is choice, i.e. that a person could have done otherwise.

Of course, if we believe that human nature is something other than the result of previous causes, then we may argue that people do have responsibility for their actions.


Immanuel Kant (1724-1804) is regarded as one of the most important philosophers ever. A major figure of the Enlightenment he tried combine both rational and empirical strands in his philosophy.

He wrote on the natural sciences, metaphysics (what reality is), morality and religion.

He was impressed with progress in the natural sciences following Newton and was concerned that philosophy in contrast was muddled and filled with disagreement. His project was to try and find if philosophy could say anything at all.

He thought that the role of philosophy was to uncover how human beings understand or categorise the world. One of his conclusions is that we make sense of the world is through categories such as space and time. We impose these categories on objects, and they are a property of our understanding rather than properties of objects.

In moral philosophy, he starts from the idea that all human beings are rational and autonomous (free to make choices). From this starting point he went on to say that universal moral laws are possible. (See categorical imperative later).

Kant would have liked to have found a sound philosophical basis for belief in God, however he found all philosophical attempts to prove Gods existence unsatisfactory (See Philosophy and the proof of God's existence). For Kant whether God exists is a question of faith rather than reason.

All western Philosophy since the Enlightenment has been coloured by Kant, and philosophers today are still actively engaged in debating his ideas.

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