Consider two famous statements associated with the 18th-century Enlightenment. The first comes from the second paragraph of the United States’ Declaration of Independence in 1776. ‘We hold these truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain inalienable rights.’ No rational person could proceed in the consideration of this without noting that the first part is complete nonsense.

If one is privy to that kind of information one might wish to say that the Creator loves all His creations equally, but it is certain that, whatever the mode and means of creation, human beings are not created equal. The blackbirds in my garden are equal. I’ve watched them for 40 years and there are no perceptible differences between them in their capacity to build nests, reproduce, forage for food, and so on. They are, within a small margin, the same size and weight. By contrast, one of the components of the essence of humanity is inequality whatever standard is invoked. We are a very diverse species biologically and, once we have language, consciousness and intelligence, the divergences magnify geometrically. Then we spend our time constantly increasing inequalities because of our constant striving for wealth and status.

The second statement occurs at the beginning of Jean-Jacques Rousseau’s Du Contrat Social. ‘L’homme est né libre et partout il est dans les fers’, normally translated as ‘Man is born free and everywhere is in chains’. In the case of the first part of this statement we are entitled to ask whether anybody has ever started a book with a more ludicrous proposition. We are born helpless, in the control of one or two potential tyrants who themselves, in all probability, are bound within structures of power and authority that they cannot change and can rarely influence. Even when interpreted phylogenetically, as being about the progression from hunter-gatherer to modern state, there is no prospect of literal truth. The freedom of the hunter-gatherer ‘noble savage’ was a poor thing and his (and her) social structures patriarchal and authoritarian.

Bertrand Russell provided the best means of understanding such statements when he classified them as ‘Sunday truths’. We spend six days acting as if water will boil if we heat it sufficiently and then we assemble in a building on Sunday to intone that water boils when it freezes. We know that the wafer biscuit does not really turn into flesh, but we say that it does and insist that there is a truth apart from literal truth. Sunday truths have been around throughout history, so they probably relate to a very deep need. The important point is that the creeds of this version of the ‘Enlightenment’ are exactly like those of established religion. Equality is logically equivalent to the immortality of the soul. It is primarily a humanist form of religion, whose Sunday truths are about Mankind rather than God, though the latter is often included anyway.

In 1748 David Hume suggested, in An Enquiry Concerning Human Understanding, that we should ask of any text: ‘Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Consign it then to the flames for it can contain nothing but sophistry and illusion.’

That is ‘Enlightenment’ in a different sense, and you do not have to know any philosophy to know that it is entirely incompatible with the statements from Rousseau and the US Constitution, which would not pass Hume’s test for even a moment. If you do know some philosophy you will probably realise that Hume’s ‘fork’ is generally considered to be too stringent a test. There are also truths that fit into neither category, what Immanuel Kant called the synthetic a priori and a more recent philosopher, Peter Strawson, the preconditions of discourse. These are the assumptions we have to make in order to have a rational or scientific discourse, the ‘uniformity of nature’, meaning the reality of discernible causation even where there is apparent randomness. They do not include ethical propositions and Hume’s fork remains a good starting point for modern, secular thinking.

There was not something we can sensibly call ‘the Enlightenment’. There were two movements of ideas, which were not merely separate but opposite in most respects. The Sceptical Enlightenment rejected religiosity completely. Its greatest figure – Hume – expressed support for the Hanoverian monarchy on the paradoxical grounds that it had no ideological justification; he was emphatic that popular sovereignty was as much complete nonsense as the divine right of kings and more dangerous. Hanoverian government was not, in many respects, good government, but it did allow a ‘system of liberty’ that was unprecedented. Voltaire’s account of Hanoverian England in Lettres sur les Anglais (pertinently called lettres rather than essais because of French censorship) emphasises with some wit that the English have lost any taste they might once have had for arguing about theology and the moral basis of government and are now preoccupied with making money so ‘the only heretic is the bankrupt’.

It is not usually remarked as such, but Adam Smith in The Wealth of Nations complements Voltaire in suggesting that, on the whole, we are collectively better off if individuals are left to pursue their own interests and that this does not have the bad consequences previously assumed. A central tenet of the sceptical enlightenment is that morals and institutions cannot be judged on their conformance to a priori principles, often called deontological philosophy, but should be judged on whether we like their consequences, an approach sometimes called (confusingly because its used in theology in quite a different way) teleology, but more simply consequentialism.

That is the assumption most fully worked out by Jeremy Bentham in his utilitarian philosophy, and he was clearly aware that it had new as well as old opponents. In particular he was virulently opposed to ‘natural’ rights – the idea that people have rights simply because they exist. To him this was the old, deontological morality revived in a new form and, in Anarchical Fallacies, he called it ‘nonsense on stilts’. Edmund Burke developed the core arguments of scepticism, arguing that the working institutions that we already have will in many cases be the best available simply because they are working, and no abstract principles can substitute for their acceptance and utility.

The principles of the sceptical enlightenment are really that there are no principles. Actions should be judged on their consequences. Governments do not rest on grand contracts or metaphysical beliefs, but arise (in Hume’s words) out of ‘usurpation and conquest’ and they, too, are to be judged on their consequences. Humanity has no pre-ordained destination; the best it can do is to avoid the errors of the past, most of which arise out of excessive religious enthusiasm. By contrast the ‘Enlightenment’ of Rousseau and Tom Paine in The Rights of Man and Thomas Jefferson and the left hand side in the French revolutionary National Assembly involves enormous amounts of metaphysical belief: human rights (as they would now be called), equality and the sovereignty of the people to a sceptical perspective are no better than the divine right of kings and the immortality of the soul. It is fair, therefore, to call this the Degenerate Enlightenment because it involves the resurrection of religiosity. Part of that religiosity is the revival of the millenarian dimension of religion, the belief in a future condition of mankind which will be near perfect: a land of milk and honey becomes Future Communism, complete equality, perpetual peace, harmony with nature, a progress which is thought to be happening at some level despite all evidence to the contrary. The need to accelerate this progress can be used to justify almost anything.

A modern, durable, intellectually defensible conservatism must be based on the arguments of the sceptical enlightenment. Equally, varieties of ‘leftism’, progressivism and idealism originate, ideologically, with the degenerate enlightenment. To put it mildly this is widely and wildly misunderstood and often subsumed under a preposterously simplistic spectrum of ‘left’ and ‘right’.

It is noticeable that though there are major political movements in the vast majority of countries that are conservative, very few of them use the name because it is tainted with pre-Enlightenment beliefs compounded in many cases by connections with Fascism and Nazism. Adding to this confusion is the fact that there are many people in the United States who call themselves ‘conservatives’, but who are actually fanciful idealists whose ideas owe little or nothing to the sceptical enlightenment.

There is a paradox of modernity. The descendants of the degenerate enlightenment usually think of themselves as ‘modern’ and ‘progressive’, whereas their ideas are really a regression to religiose philosophical indiscipline. It is the conservative political thinkers, the descendants of the sceptical enlightenment, who are truly modern. It should be noted that it is entirely possible for a conservative to agree with progressive causes such as the empowerment of women or particular ethnic groups – because they are a good idea in terms of the general wellbeing, not because they are progressive or modern. In the same way one can welcome universal suffrage not because ‘democracy’ is an essentially superior form of government, let alone because it represents popular or any other form of sovereignty, but because it functions as a necessary mechanism for getting rid of particular governments. In a similar way, Hume’s argument for the Hanoverian style of monarchy still stands; republics rest on too much ideology and self-righteousness.