The relationship between John Locke and Isaac Newton, his co-founder of, in the apt phrase of one recent writer, ‘the Moderate Enlightenment’ of the eighteenth century, has many dimensions. There is their friendship, which began only after each had written his major work, and which had its stormy interlude. There is the difficult question of their mutual impact. In what ways did each draw intellectually on the other? That there was some debt of each to the other is almost certain, but its exact extent is problematic. Questions may be asked over a whole range of intellectual issues, but not always answered. Thus their theology, which was in many respects close, and which forms the bulk of their surviving correspondence, may yet reveal mutual influence. There is the question of their political views, where both were firmly Whig. But it is upon their philosophy, and certain aspects of their philosophy in particular, that this paper will concentrate. My main theme is the nature of their empiricism, and my main contention is that between them they produced a powerful and comprehensive philosophy.

In a celebrated passage in ‘Of the Standard of Taste’, Hume tells us that those readers who prefer Bunyan's writings to Addison's are merely ‘pretended critics’ whose judgment is ‘absurd and ridiculous’; this is ‘no less an extravagance, than if he had maintained a mole-hill to be as high as TENERIFFE, or a pond as extensive as the ocean’ (GG, iii, p. 269). Hume shows a decisiveness and vehemence in his judgment against Bunyan that has greater significance than that of being a mere reflection of his aesthetic principles. Hume does, after all, wish to make ‘durable admiration’ the foundation of his standard of taste, and both the number of eighteenth-century reprints of The Pilgrim's Progress and Johnson's comment that this work has as ‘the best evidence of its merit, the general and continued approbation of mankind’ testify to the lasting popularity of Bunyan's work (GG, iii, p. 27i). Hume's critical judgment on Bunyan is not merely a consequence of a mechanical application of his standard of taste, but is rather a reflection of what I will term Hume's ‘epistemology of ease’.

My title advertizes a paradox. The characteristic complaint of the sceptic is that others make assumptions they are not entitled to make. A philosophical sceptic is committed to a systematic refusal to accept such assumptions in the absence of the kind of justification they think is required. A sceptic who, none the less, helps himself to such an assumption, seems to be caught in a paradoxical position. This is the kind of situation in which, it seems, certain eighteenth-century sceptical philosophers were placed in relation to the ‘principle’ of natural order. They did not doubt that there is such a principle, that there is a source or ultimate cause of the order to be found in the universe. And yet, on their own terms, is not the existence of such a principle something we should expect them to have doubted? What I shall try to do in this lecture is to bring out why they did not doubt the existence of such a principle and how serious their failure to do so is for their sceptical position.

What darkness was the ‘Enlightenment’ supposed to have removed? The answer is irrational forms of religion. Most of the ‘enlightened’ took the view that revealed religion was irrational and that natural religion could be rational; but some were sceptical about natural religion too. Hume was the most honest and the most penetrating thinker of the latter group. His biographer, Professor E. C. Mossner, is not alone in believing that the Dialogues concerning Natural Religion is ‘his philosophical testament’.

The term ‘Scottish Enlightenment’ annoys some Scottish historians, because to them it seems to suggest that a state of unenlightenment prevailed in Scotland before the mideighteenth century, but ‘enlightenment’ when used by the historian of ideas is simply a technical term to describe certain aspects of eighteenth-century thought. The trouble is in defining precisely what aspects of eighteenth-century thought it is meant to describe. Different people study the eighteenth century Scottish thinkers for different reasons; for Professor Pocock, for example, they belong to the tradition of ‘civic humanism’ and constitute one of his Machiavellian moments. But they are more widely known nowadays for the modernity and sophistication of their social theory.

From the time of its clearest origins with Pascal, the theory of probabilities seemed to offer means by which the study of human affairs might be reduced to the same kind of mathematical discipline that was already being achieved in the study of nature. Condorcet is to a great extent merely representative of the philosophers of the seventeenth and eighteenth centuries who were led on by the prospect of developing moral and political sciences on the pattern of the natural sciences, specifically physics. The development of economics and the social sciences, from the eighteenth century onwards, may be said in part to have fulfilled and in a manner to have perpetuated these ambitions. In so far as the new sciences have been susceptible of mathematical treatment, this has not been confined to the calculus of probabilities. But there is a temptation at every stage to ascribe fundamental significance and universal applicability to each latest mathematical device that is strikingly useful or illuminating on its first introduction. It is the theory of games that enjoys this position at present, and shapes the common contemporary conception of the very same problems that preoccupied Condorcet.

In this paper I want to discuss David Hume's views about morals, politics and citizenship and the role of philosophers and philosophizing in modern civil society - what I shall call his theory of civic morality. This is a subject which has been neglected by philosophers, presumably because it is of limited philosophical interest. But it is of considerable interest to the historian who wants to understand Hume's development as a philosopher, to locate his thought within a specific, Scottish context and to arrive at some understanding of his surprisingly close and cordial relations with the literary and social world of enlightened Edinburgh. These are large claims and I cannot hope to substantiate them fully in a short paper. My purpose is first, to show that, historically speaking, Hume's preoccupation with civic morality was of central rather than peripheral interest to him as a philosopher and that it helps to explain his otherwise rather puzzling decision to give up philosophizing systematically in the manner of Hobbes and Locke, in favour of polite essay-writing in the manner of Addison and Steele. My second purpose is to suggest that Hume's interest in civic morality, his neo-Addisonian (or perhaps I should say, neo-Ciceronian) mode of philosophizing about it and the nature of his understanding of politics, citizenship and philosophizing in a modern age was, unlike his thought about religion, responsive to and consonant with some of the most important ideological preoccupations of his Scottish contemporaries. It was, I suspect, a shared interest which helped to contain some of the anxieties Hume's notorious religious scepticism caused his contemporaries. Without it, he could not possibly have emerged as one of the leaders of Edinburgh's intellectual life in the age of the Scottish Enlightenment.

Principal editor of the great Encyclopedia, novelist and prose writer of genius, contributor to the development of scientific thought and method, to the theory of the bourgeois drama and to the practice of art criticism, Diderot perhaps embodies the rich variety of the Enlightenment spirit more than any other man. His only real rival is surely Voltaire. Rousseau, whose influence was greater than Diderot's, would not thank us for classing him among the philosophes. The more profound philosophers - a Hume or a Kant - not only lack his range, but are less unquestionably ‘Enlightenment men’.

From the very outset of his literary and intellectual career Rousseau saw himself as an uncompromising critic of contemporary society. As he has vividly related in his personal writings, the famous moment of ‘illumination’ when he was on the way to visit his friend Diderot imprisoned in the Chateau de Vincennes not only gave him a vision of ‘another universe’ but transformed him into ‘another man’. An overwhelming ‘enthusiasm for truth, freedom and virtue’ made him henceforth reject the corrupt values of the society he saw around him; ‘to be free and virtuous and above fortune and opinion’ seemed a greater and nobler attitude than servile acquiescence in the ‘maxims of his age’.

It is something of a commonplace of Butlerian interpretation that the main interest and achievements of Butler's moral philosophy are in normative ethics, and not metaethics. He wishes to bring moral enlightenment to citizens and not, to philosophers, epistemological enlightenment. Nonetheless for that he makes a number of remarks which, if we were collecting for some bizarre purpose metaethical forms of words, we would note down and include in our collection. Thus he makes some progress towards the development of a moral epistemology, a theory of moral judgment. My purpose here is to assess those steps, and to see how far the structure which results can be called a theory. I have the impression that much of the reluctance among scholars to allow that Butler does have a theory of moral judgment is caused by the metaethical blinkers that they themselves wear; what is in fact the beginnings of an unfashionable and unconventional theory is seen as unsophisticated confusion. But I shall not overdo praise of Butler. I shall suggest that Aristotle does a somewhat better job of developing this type of theory.

‘I see well enough what poor Kant would be at’ said James Mill on first looking into the Kritik der reinen Vernunft. No one would wish to say that the reception of Kant in England has remained at this level: abundance of sound scholarship, innumerable Kant seminars and the swell of interest in transcendental argument which has developed since the Second World War all exist to prove the contrary. But in spite of all that, Mill's response still touches a chord in English breasts. We are prone to think Kant a conjurer. If we are to accept, or even to work seriously with, any version of Kantianism it must be a demythologized, logically aseptic version. Strawson's Kant, for instance, is a Kant freed from the ‘strained analogy’ between the study of the conditions of sense, or intelligibility, and the study of the human cognitive system. And in moral philosophy too, the English Kantianism chiefly represented by the work of Professor R. M. Hare has scrupulously avoided those parts of Kant's ethics which have a suspiciously speculative flavour: the notion of an unqualified good, for example, or that of treating moral agents as Ends-in-Themselves; and more generally the whole notion, which permeates Kant's moral philosophy, that morality can only ultimately be understood in terms of a set of ideal relationships that entirely transcend all considerations of common-sense mutual accommodation or rational self-interest: transcend all such considerations so radically, in fact, as to point mutely towards the possibility of a life after death.