The Enlightenment: a Summary

The Enlightenment is a way of thinking that is free from dogmas and based on reason and experience. The Age of Enlightenment marks the period when this way of thinking came about in the second half of the eighteenth century, although its roots go back much further, to the transition between the Middle Ages and Modernity. Some of the main transition thinkers at this time were: Nicolaus Copernicus (1473-1543), Tycho Brahe (1546-1601), Francis Bacon (1561-1626), Galileo Galilei (1564-1642), Thomas Hobbes (1588-1679), Johannes Kepler (1571-1630), René Descartes (1596-1650), Benedictus Spinoza (1632-1677) and John Locke (1632-1704). The end of the Age of Enlightenment has been demarcated to coincide with the end of the 18th century, although this did not mean the end of the ideas of the Enlightenment.

Part of the Enlightened mindset was to keep the secular separate from the religious and this was the norm among the practitioners of the objective sciences of Physics and Mathematics that dominated the era. Of all the philosophers of the Enlightenment, the most prominent was Immanuel Kant, a Prussian from near Königsberg (now Kalingrad, a Russian village), an epistemologist and political philosopher who understood and accepted the separation between the secular and the religious even though he believed in God.

Kant on Free Will and Perpetual Peace
Immanuel Kant was a firm believer in man’s free will as opposed to the counter idea of determinism. In order to explain his views, Kant used the word ‘phenomenon’ as a translation of the German word ‘Erscheinung’, which literally means ‘appearance’, to describe the immediate object of sensory intuition, meaning the bare information about an object interpreted through substance and cause. He called the ‘thing-in-itself’ the ‘noumenon’, the last reality. As a being of ‘phenomenon’ or the senses, man’s volition and action are under the control of natural necessity; as a being of ‘noumenon’ or the ‘thing-in-itself’, man is free.

The only significant flaw in Kant’s work is that he was overly optimistic regarding scientific progress, namely that it could lead to a progressive and peaceful world culture. Kant’s optimism was based on a brief period of peace which followed the Treaty of Basilea between Prussia and France. He had seen a lot of war in his time and this interval of peace inebriated him to create a utopia of perpetual peace for humanity. Kant revealed his ideas of political philosophy in a 1785 essay called Perpetual Peace, where he described the world progressing towards an ideal society in which reason would ‘bind every lawgiver to make his laws in such a way that they could have sprung from the united will of an entire people, and to regard every subject, in so far as he wishes to be a citizen, on the basis of whether he has conformed to that will’. Along with the idea of perpetual peace, Kant recognised the unity of the human race and introduced the idea of a world federation of republican states and global citizenship. This is why Kant’s utopia became known as Universalism.

There was another optimism in the Age of Enlightenment which was even more overstretched than Kant’s universalism. This optimism was the expectation that there were laws of society to be discovered, just as the natural laws of the movement of the planets. This belief was widespread among scholars who were not mathematicians and physicists such as the young Napolitan historical philosopher Giambattista Vico (1668-1744). Kant’s Critique of Judgement, providing guidance on how to give objectivity to the study of the natural world and the humanities, delivered an implicit message to such scholars that there is no such thing as ‘natural laws of society’.

Disagreement About God and Other Things
Although the set of ideas associated with the Enlightenment shared common ground this does not mean that the philosophers of this period all thought alike. The main thing that separated enlightened thinkers was their belief or lack of belief in God. The majority appear to have been deists or agnostics and only a few were declared atheists. Immanuel Kant affirmed that he never doubted the existence of God and yet he rejected the idea of intelligent design and stressed that there is no rational justification to ascertain dogmatically that God exists. Kant’s ambivalence1 regarding God was not uncommon among the enlightened thinkers. The most notorious enlightened atheist was Baron d’ Holbach (Paul-Henri Diedrich, 1723-89), a French encyclopaedist and philosopher, whose atheism is proclaimed in his major work The System of Nature (Système de la nature) of 1770.

The New Isms
Apart from God, the other main disagreement among the enlightened thinkers are all described by ‘ism’ words such as materialism, mechanism, naturalism, determinism and idealism. Materialism refers to the view that all facts are caused by physical processes alone and can be reduced to them. The main contentions of materialism are denial of free will, God and the inclusion of mental processes. Mechanism is a form of Materialism that holds that natural phenomena can only be explained by reference to matter and motion and their laws. Naturalism states that everything is natural and fall under the ‘laws of Nature’, which can be uncovered through scientific investigation. Determinism is the belief that man does not have free will because all of his moral choices are determined by previously existing causes. Idealism was understood by Kant as ‘the ideal of pure reason’ but a more radical form of idealism was introduced later by the Irish-born philosopher George Berkeley (1685-1753) who stated that only thought or ideas form the fundamental reality (see below).
The above mentioned D’Holbach, upheld an atheism that was accompanied by ‘materialism’ of the ‘mechanistic’ kind which also happened to be deterministic. In d’Holbach’s interpretation, thought is something that comes from hidden motions inside the body and morality results from the physical tendency of self-preservation. Thus, d’Holbach turned man into a ‘machine’ devoid of free will, where the forces of the soul are no other than those of the body. D’Holbach’s combination of atheism with materialism triggered the dismissal of both, putting on hold any serious discussion of atheism per se.

Nature and the Laws of Nature
The word ‘nature’ was used in the eighteenth century to refer to all that exists, that is, both the universe as a whole and the earth and the species on it. This led to the assumption that there were ‘laws of Nature’ about everything including society, and that the object of science was to discover them. However, laws of Nature such as gravitation and the laws about the movement of the heavenly bodies are commonly restricted to the science of Physics. Kant’s categorization of Nature into ‘phenomenon’ and ‘noumenon’ also served to explain why certain things within Nature have natural laws and others don’t. Thus, according to Kant, those parts of nature that are perceived as ‘phenomenon’ are mechanistic and ruled by natural laws; the remaining parts are complex systems which need to be studied differently. From the nineteenth century onwards, the word ‘cosmos’ started to be used to refer to all that exists, while the word ‘nature’ acquired its present connotation of the earth and living organisms. The old expression ‘laws of nature’ was changed to ‘laws of the universe’ or ‘laws of cosmology’.

The Enlightened Political Science
A new political science emerged in Europe during the Age of Enlightenment, being less functional and more theoretical than classical political philosophy. Its main concern was method, utilising the technique of contrasting one thing against one or more alternatives such as ‘the civil state’ versus ‘the state of nature’, ‘facts’ versus ‘values’, ‘realities’ versus ‘ideologies’, ‘the world’ versus ‘the world of different societies’ and even the contrasts between the ‘I, me, thou, and we’. The aim of the new political science was to develop the capacity to form a political structure of some kind, such as a legislator seeking compromise between what is desirable and what the circumstances permit. It also aimed to deal with the internal as well as external issues of a political unit such as a city or a nation. While classical political philosophy attached importance to debating the merits of different types of political orders (forms of government), the main concern of the new political science was to define the various political orders that existed,without passing value judgement.
One of the greatest political philosophers of the Enlightenment was Baron Charles de Montesquieu (1689-1755), who analysed the ideas underlying the various laws throughout history. His proposed form of government, based on the separation of powers – legislative, executive and judicial, became the model for all constitutional democracies of the West.

The Counter-Enlightenment
The Enlightenment and all the optimism that it brought began to attract bad publicity when the peace that Kant had envisaged did not materialise. First came the wars of the French and the American republics and then the Napoleonic wars. These wars provided an opportunity for terms such as mechanism, materialism and atheism to be used as scapegoats, as the sweeping changes brought by the Enlightenment proved too much for the many who would have preferred to leave things as they were. A Counter-Enlightenment soon emerged, doubting the outcome of a secularised science, independent from religion.
The Counter-Enlightenment refers to all the movements against the rationalism, universalism and empiricism associated with the Enlightenment, which appeared from the late eighteenth century. The best known counter-Enlightenment movement was the Romantic Movement, characterised by a mindset, present mostly in the arts, which sought to restore the age innocence taken away by the ‘mechanistic science’ of the Enlightenment. The term ‘Idealism’ is sometimes used to describe a mindset centred on imagination, nature, symbolism and Divine Providence, and this can equate Idealism with the Romantic Movement. However, in philosophy, the Romantic Movement and Idealism are two different things.

The Romantic Movement
The Romantic Movement in philosophy started with Jean Jacques Rousseau (1712-78), who wrote in the areas of society and education. With regards to society, Rousseau was highly critical of modern science and modern society and promoted a return to a distant past when things were more genuine and uncorrupted. Rousseau’s perfect society was founded on liberty, equality and fraternity and was based only on the general will, ignoring the views of minorities. Thus, his proposition that every issue could be solved by a vote of the citizenry led to the absolute rule by the majority, something that the French revolutionaries later introduced. With regards to education, Rousseau wanted a return to the state of nature, when man supposedly lived without the corrupting influences of society. However, he contradicted himself when he stated that ‘man’s nature is not fully mature until it becomes social’ as well as in proposing an egalitarian society from which women were excluded. In his La nouvelle Héloise, Rousseau tried to show that women need to develop instinct and feeling in order to be effective companions to their husbands.

The philosophy of Idealism stemmed from the Enlightenment in the 1770s when Wilhelm Leibnitz (1646-1716) introduced his theory of Monads, the building blocks of every object, which God created to give sense to the world. Although the theory of Monads is considered a wacky idea by today’s standards, Leibnitz can be viewed as an enlightened philosopher who defended rationalism and shared the optimism of Kant. As already mentioned, Berkeley took this idea forward and stated that the only reality is ‘thought’ while all that exists – the things and objects perceived by our senses – are not real. Several great philosophers became associated with Idealism, the main ones being Georg Hegel (1770-1831), Friedrich Wilhelm Joseph Schelling (1775-1820) and Johann Fichte (1762-1814).

Science in the 19th century
The separation of the secular and the religious that characterised the Enlightened mindset appeared to have vanished by the 19th century. There is plenty of evidence for that in the countless wrong conclusions that the natural historians took due to their belief in creationism. Had the Enlightened mindset vanished or was it simply hidden behind the Romantic ideas? The answer to this question can be found in a hindsight analysis of the kinds of science practised in the second part of the 18th and the first three quarters of the 19th centuries. While the former was dominated by the exact sciences, the latter was dominated by non-exact ones such as psychology, geology, botany, zoology and biology.

The separation of the secular and the religious was easy for the exact scientists working with the cosmos but proved difficult for the non-exact scientists whose objects of study were closer to home. This is not to say, however, that all non-exact sciences were characterized by a lack of objectivity. Statistics began to develop at that time as a tool to add objectivity to the subjective nature of the various new sciences that appeared. In spite of that, it is fair to say that many non-exact scientists and the scholars working in the humanities were dilettantes who lacked the disposition to question everything, as did the 18th century physicists. It is also fair to say that most of them did not practise their science with an unprejudiced mind.

When the Swedish botanist Carl Linnaeus (1707-78) set himself the task of classifying the flora of the world, with the help of an army of plant collectors around the globe, he thought he was completing the job of the biblical Adam. Therefore, when he inspected his garden, planted according to perceived kinship relations, and saw gradations instead of clear cut separations between species, the idea of evolution still did not occur to him. Something similar happened when the French zoologist Baron Georges Cuvier (1769-1832) compared the analogous parts of the anatomy of various animals both living and extinct and still insisted in creationism. Cuvier’s theory of catastrophes to explain the extinct fauna shows that he was not studying nature with an unbiased mind but with a mind committed to religion. The doctrine of creationism was finally disproved by the British naturalist Charles Darwin (1809-82) in his 1859 book The Origin of the Species, describing how life on earth evolved over millions of years through a process of adaptation and natural selection.

Although the subject of chemistry started with Robert Boyle’s discovery of phosphorous in 1649, thus at the start of the Age of Enlightenment , it was during the 19th century that it came of age, with the publication of the periodic table by Dmitri Mendelev in 1869. The fact is that the exact sciences did not disappear during the 19th century. They just weren’t that noticeable amid the many other subjects that were developing at the time. In physics, a crisis was created after the recently discovered electromagnetic force appeared to conflict with gravity. This crisis was resolved only in the twentieth century by Albert Einstein’s two theories of relativity.

The Enlightenment’s New Enemies
In the 20th century the Counter-Enlightenment came not just from religious dogmatism but also from Post-Modernism. By Post-Modernism I do not mean the kind defined by The New Oxford Dictionary as “a late 20th century style and concept in the arts, architecture, and criticism, which represents a departure from modernism and has at its heart a general distrust of grand theories and ideologies as well as a problematical relationship with any notion of ‘art’.” but to the relativist ideology which stemmed out of literary criticism during the last quarter of the 20th century, centred on the idea that the universal realities of the world are social constructs based on language and communication, and for that reason can be fixed simply by a change of meaning. There is a sweeping assumption in this idea, namely that one type of opinion is as good as another, and that there is no such thing as ‘best knowledge’ or ‘scientific knowledge’.

The inter-related concepts of social construction and linguistic idealism were at the centre of the American culture wars, according to Ian Hacking, a Canadian professor of philosophy at the University of Toronto and winner of the Holberg Prize in 2009. According with K J Gergen, social construction is a perspective which believes that a great deal of human life exists as it does due to social or interpersonal influences. According to Hacking, linguistic idealism refers to the doctrine that only that which is talked about exists. In Hacking’s view, sorting out the culture wars required some kind of mediation from individuals who had the cognitive skills to understand the problem and were willing to get involved.
Although it can be argued that for a large part of the twenty century the Enlightenment appeared to remain eclipsed, it also can be argued that the Enlightenment’s ideas were there all the time. They persisted, not just in the minds of the people who accepted that there is a ‘best knowledge’ in the kind of knowledge derived from reason and from science, but also on the expectations of the general public who looked to science and technology to improve their lives.
Jo Pires-O’Brien is the editor of PortVitoria, a cultural internet magazine dedicated to the Spanish and Portuguese speaking communities worldwide:

1. Kant’s ambivalence regarding the existence of God was my interpretation based on what I read from Kant himself. However, Will Durant in his book The Story of Philosophy (1953) states that Kant did not press his conclusion regarding God for he realised that the world was not ready for it. Durant also pointed out that Kant wrote his Critique of Pure Reason not to put down science but to show its limitations, something that he had to do in order to demonstrate that religion cannot be proved by theoretical reason. ‘Transcendental dialectic must remind theology that substance and cause and necessity are finite categories, modes of arrangement and classification which the mind applies to sense-experience, and reliably valid only for the phenomena that appear to such experience; we cannot apply these conceptions to the noumenal (or merely inferred and conjectural) world. Thus, Kant concluded his Critique, stating that the objects of faith – a free and immortal soul and a benevolent creator, could never be proved by reason. According with Durrant, those who understood the message at the end of the Critique of Pure Reason realised straight way that Kant had undermined the most precious argument of theology and thus killed God.

Gergen, K J (1985). The social constructionist movement in modern psychology. American Psychologist, 40(3), 266-275. In: Ian Rory Owen’s Social constructionism and the theory, practice and research of psychotherapy: A phenomenological psychology manifesto. 28 p. (
Hacking, Ian (1999). The Social Construction of What? Harvard University Press, Cambridge. 261 p.
Kant, Immanuel (2005). Critique of Judgement. Translator: J H Bernard. Dover Publications Inc, Mineola, New York.
Montesquieu, Charles de (1986). The Spirit of Laws. In: Maynard Hutchins, Robert, Editor in Chief, Great Books of the Western World 38. William Benton, Publisher, Chicago.
Vico, Giambattista (2008). A Ciência Nova. In:Gardiner, Patrick, editor, Teorias da História; Interpretação do Processo Histórico. 6ª edição.Fundação Calouste Gulbenkian. Lisbon.

Acknowledgement: Helen Kirby, revisor

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