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David Hume - Study Notes

HUME by A.J. Ayer

This book was first published by the OUP in 1980 which was, I believe, before the Very Short Introduction Series was established. The author, Sir Alfred Ayer, was himself a philosopher of note in the 20th Century. Born in 1910, his initial claim to fame was as author of Language, Truth and Logic which came out in 1936, and a very controversial and influential book it was too. It’s still in print, as a Penguin. It set out the radical philosophy of Logical Positivism as originally formulated by a group of eminent German and Austrian physicists, philosophers, logicians and mathematicians in the 1920’s.

David Hume, the Scottish philosopher who lived from 1711 to 1776, anticipated many of their ideas. He was and still is one of the most important philosophers of modern times. I shall follow the convention of regarding ‘modern times’ as having started, very roughly, from about 1600 onwards. Ayer commences his book with a brief outline of David Hume’s life, noting that he was born into the ‘middle gentry’, received a university education at Edinburgh but interestingly, never held an academic post during his career (probably because of his agnosticism). In fact for many years he achieved greater fame not as a philosopher but as a historian with his History of Great Britain, and he also pursued a successful diplomatic career for some years.

His most important publications included A Treatise of Human Nature, 1739, Essays Moral and Political, 1742, Enquiry Concerning Human Understanding, 1748, Enquiry Concerning the Principles of Morals, 1751 and the Dialogues Concerning Natural Religion, published posthumously in 1779. In this last work he incisively criticized certain arguments purporting to prove the existence of God which he considered to be fallacious.

I don’t think it’s necessary for me to reiterate Ayer’s account of Hume’s life in any detail; in fact I think it’s equally interesting to appreciate the historical era into which David Hume was born, in 1711. For the preceding century, the seventeenth, had been the century when modern science began to ‘find its feet’. Of course, most ordinary people in those days were still as ignorant and superstitious as they had been in mediaeval times. People still believed in imps, demons, hobgoblins, ghosts, spirits and what have you, but within the world of learning, great changes had been taking place ever since the Renaissance during the fifteenth and sixteenth centuries.

The middle ages had been an age of scholasticism. ‘Knowledge’ was acquired through diligently studying the ancient writings, these being the Holy Scriptures plus the works of the ancient Greek philosopher, Aristotle. But scholasticism began to change. It came to be realized that through observation and research, the world was round, not flat. It came to realized that the world we inhabit is not the centre of the universe. It came to be realized that you could observe distant objects up in the sky through telescopes. You will all be familiar with such famous names as Galileo, Kepler and Copernicus. The ‘world-view’ began to change, radically and dramatically, once people started observing the world around them instead of sitting in a library studying the ancient writings. This was how knowledge was acquired – through observation and experiment. Ironically, Aristotle would probably have been the first to applaud this process, and the first to have condemned the ossification in mediaeval times of his own early scientific work.

One of the most important and influential works ever to be published was Francis Bacon’s “The Advancement of Learning” which came out in 1605. To put it in a nutshell, Bacon said that if you want to acquire knowledge and understanding, don’t waste your time perusing ancient books. Go out and have a look at things for yourself – make observations, measure things, carry out tests, repeat your experiments, record the results in detail, seek out explanations for what you observe, devise theories and, most importantly, develop criteria to test one theory against another one. Bacon was in fact the first modern writer on scientific methodology or, as it is often called, the Philosophy of Science.

So, men of learning followed his precepts and began to acquire knowledge which had a degree of precision that was previously unknown. They began to distinguish between astronomy which was science and astrology which was not science, between chemistry on the one hand and alchemy on the other. They began to realize that a theory which has been properly researched can be relied upon to forecast future events (such as the exact location of the planet Neptune in five years’ time), and they started to abandon ancient methods of foreseeing the future such as fortune telling, reading the Tarot cards, necromancy and so on. Of course, it wasn’t all plain sailing; there wasn’t an abrupt change from ancient superstition to modern science; there was a lot of overlap. Even Sir Isaac Newton, the great scientist, still believed in witches (!).

The seventeenth century saw an explosion of human knowledge and of invention. Notable discoveries included the speed of light, the laws of gravitation and the development of differential calculus in 1665 which ushered in higher mathematics. Notable inventions in the seventeenth century included the microscope, the barometer, the thermometer and many others. By the year 1700 science ‘had arrived’ and the modern world-view, within the major centres of learning at any rate, had come into existence. It became established and began to permeate, over time, through to educated people more generally. Of course, religion was still firmly established and so was metaphysical philosophy, but this was the changing world into which David Hume was born, and his philosophy reflects the modern outlook. So let us now turn to David Hume’s philosophy as set out in Ayer’s book.

If I had to sum up Hume’s philosophy in one single word, it would be ‘empiricism’. Nothing to do with empires or imperialism, the word ‘empiricism’ means, in a nutshell, that knowledge can only be based, ultimately, upon what we perceive, observe, or experience, through our five senses – what we see, hear, touch, taste or smell. The most usual term for this is ‘sense-experience’. This can of course be aided by instrumentation or by other aids (such as telescopes, microscopes or spectacles). It is also ‘legitimate’, so to speak, to acquire knowledge through what other people tell us, through books and so on, providing we have no good reason to doubt their veracity and trustworthiness. We can acquire knowledge ‘second-hand’ through other people’s sense-experience, but the critical thing is that ultimately, knowledge can only come from someone or other’s sense-experience.

Hume’s point was a very simple one. He asked how can we possibly know anything beyond sense-experience if all we can possibly observe is only through sense-experience? If our starting point is – as it must be – a set of statements about what is observed through sense-experience, then any statement we try to infer which goes beyond what is observed through sense-experience must necessarily be an inference that does not follow – that is, a non-sequitur. For example suppose we say that the universe and everything in it must have had a designer, or Creator. The problem is that all we can observe is the universe and what’s in it; we have never, as yet, observed a designer or Creator ‘outside it’, so to speak. This is not to say that there isn’t one; it is simply not proven. And for exactly the same reasons he rejected metaphysical talk about ‘first causes’, ‘ultimate causes’ and so on.

The only a priori ideas that Hume allowed, independently of observation or valid inference from observation, were what he called relations of ideas that are true by definition of the terms within them. Sentences such as ‘blue is a colour’, ‘all women are adult female human beings’ are true by definition and do not need to verified by observation or further enquiry. They are tautologies, often called analytic statements. Mathematical statements (such as ‘2+2=4’) are also analytically true by definition of the terms within them. By contrast, sentences such as ‘some women vote Labour’, ‘not all newspapers come out on Sundays’ are not true by definition and need to be validated through empirical enquiry.

It is important to note that Hume was not, of course, the first empiricist within the history of philosophy. He had many predecessors, some going back to ancient times. In modern times I have already mentioned Francis Bacon; other empiricists included the English philosopher John Locke (1632-1704) and the Irish philosopher George Berkeley (1685-1753). There were, of course, different formulations of empiricism as between Hume, Locke and Berkeley which Ayer discusses in some detail.

Locke’s view was that knowledge derives from our perceptions through our senses of the world around us. Basically this is the commonsense view. Berkeley did not agree, pointing out that if all we can be aware of is our perceptions, then strictly speaking we have no warrant for believing that there are physical objects corresponding to our perceptions – that is, physical objects which exist whether we are perceiving them or not. And what if our perceptions are all one big illusion? In Berkeley’s view they require ‘external’ justification, but this can only come through the agency of God who created everything.

In Hume’s view this was absurd. The idea of God does not answer the problem, it only raises another one, a big one at that: how can we know that God exists? If we cannot even know for certain that physical objects exist, how can we know there is a God? In Hume’s view all we can be aware of with any certainty is a series of ‘perceptions’; we can only assume there is an objective reality that corresponds to them. Strictly speaking, we have no more reason for thinking that there isn’t such a reality than we have for thinking that there is. But as Ayer says, the question of external objects is ‘a serious problem for Hume’. It is not clear from Ayer’s account whether Hume succeeds in giving a viable answer.

Ayer’s discussion of all these issues in Chapter Two is somewhat meandering and I think his book presupposes some familiarity on the part of the reader with the work of Locke, Berkeley and Hume. It may not, therefore, be the best introductory work to the views of those philosophers, but let us proceed all the same.

In view of Berkeley’s reliance in his arguments upon the existence of a God, Ayer mentions some of Hume’s counter-arguments against the idea of a God. For example if human beings and the way they behave is the creation of a deity, then it follows that the deity itself must be the ultimate ‘author of sin and moral turpitude’. Ayer was as much of an agnostic as Hume was, by the way.

But I don’t think that Hume ever gave a ‘hard and fast’ answer to the problem of perception. If pressed, I’m sure he’d probably have said ‘look, there’s no good or compelling reason for us to seriously doubt the reality of what we perceive. Maybe our senses deceive us some of the time as with dreams or mirages and so on, but it doesn’t follow that they deceive us all of the time.’

Hume divided perceptions into two broad categories, impressions and ideas. An ‘impression’ is when we have images of external objects conveyed to us by our senses or, secondarily, when we feel an emotion or a ‘passion’, as he called it. An ‘idea’ comes into being when we reflect on an image or a feeling, or on an object which is not present.

Ayer continues his discussion of Hume’s account of perception in Chapter Three. A major difficulty which Ayer encounters is trying to clarify what exactly Hume’s views were, where the evidence is conflicting depending upon which of Hume’s various works you refer to. There is ample evidence within his writings that he accepted the existence of physical material objects whose existence was independent of our perceptions of them. Examples include houses, books, trees, our own bodies and those of others. But his account of the causes of our beliefs in these various entities is, as Ayer puts it, ‘thoroughly confused’ (p46). He therefore seems to oscillate between firm belief in external objects and scepticism.

What Ayer seeks to do in Chapter Three is, I think, to ‘fill in the cracks’ in Hume’s account of perception which did seem to change over time. He does this by using ideas which were in fact implicit in Hume’s own reasoning all along. For example, if ‘real bodies have a continued and distinct existence, whereas perceptions are dependent and fleeting’, are they ‘dependent and fleeting’? Arguably, on Hume’s own account, they are not. Successive perceptions of an object often have a constancy and a close resemblance to each other, and to say it is false that they relate to the same object because of differences of perspective and so on is to use what Ayer calls ‘the dubious argument from illusion’. Hume also speaks of coherence from one set of perceptions to another, which gives us what Ayer calls ‘spatio-temporal continuity’. It is arguable, I think, that Ayer saves Hume from scepticism by adducing arguments which Hume himself used all along.

Ayer concludes this rather difficult chapter with a few comments on Hume’s thoughts about personal identity. To summarize, Hume expresses a scepticism which Ayer does not share. Hume equates personal identity with the identity of the mind, but when he analyses this notion he does not find grounds for believing in a ‘self’ as a ‘single unchanging object’. This is because when he ‘introspects’, he only finds some particular thought or perception or another, so that ultimately he can only conceive of the ‘self’ as a ‘bundle or collection’ of different perceptions. Although Ayer follows Hume’s line of reasoning perfectly clearly, he disagrees with Hume in the end because of one key factor, namely our own bodily continuity in space and time, which we are of course aware of. That, in his view, is an essential feature of what constitutes personal identity, and he augments it to Hume’s observations.

Chapter Four, Cause and Effect, is yet another complex account of a difficult subject-matter which looks as if it is addressed to a reader who already has some familiarity with Hume’s philosophy. I am therefore going to give a briefer account of Hume’s views which is not, I hope, contrary to Ayer’s account.

Let us take as our starting point the sentence ‘every event has a cause’. True or false? Firstly, is it a necessary truth? It cannot be, because the only sorts of sentences that are necessarily true (this is a technical term, by the way) are tautologies such as ‘2+2=4’, ‘a woman is an adult female human being’ which, like all other tautologies, are true by definition. But the sentence ‘every event has a cause’ is not a tautology; it is not true by definition. It is a defining characteristic of tautologies that their denial always results in a self-contradiction, but it is not self-contradictory to say ‘not every event has a cause’ or ‘some events do not have causes’. Therefore the sentence ‘every event has a cause’ cannot be a necessary truth, which Hume made very plain (refuting the view of the 17th century French philosopher Descartes who thought it was a necessary truth).

So, is the sentence ‘every event has a cause’ a contingent truth (another technical term) whose veracity depends upon observation? To illustrate, the truth of the sentence ‘Bob ate curry last night’ depends upon whether I did so or not; the sentence could be false, its denial is not self-contradictory so it is not a necessary truth. It is contingent. So, what about the sentence ‘every event has a cause’? Hume pointed out that the cardinal difficulty is very simply that we have never observed every event and probably never will. Some months back I saw a young theologian on television earnestly defending creationism. He said, ‘Scientists tell us that the universe started with a Big Bang – but what caused that? Something must have caused it....’ but at that point David Hume would have said, ‘Stop right there, young man! You cannot say something must have caused it, for you can never be certain that every event has a cause because you’ve never observed every event and you never will’.

Having rejected the notion of necessity Hume considers the notions of priority, contiguity and regularity in space and time as sufficient to give us a viable account of causality. To say of two things or events x and y that x is the cause of y reasonably requires that x should always precede y and that x and y should be contiguous in space and time. But priority, contiguity and regularity are not sufficient for there to be a causal relationship; counter-instances can easily be found, and many situations are so complex as to require further and highly detailed research. Hume’s scepticism therefore remains, and he concludes that our concept of causality is derived from our habitual associations between successive ‘perceptions of the mind’. To say that x causes y means that in our limited, finite experience they are observed to have a ‘constant conjunction’ to which we become habituated. So to ascribe ‘causality’ is a habit of the mind, and nothing else. It is always subject to revision in the light of future experience.

In Chapter Five Ayer summarizes Hume’s views on Morals, Politics and Religion. He begins by noting that although Hume denied that ‘every event has a cause’ was a necessary truth, he nevertheless noted on purely contingent grounds that within the realm of nature we notice sufficient regularity to lend support to the thesis of determinism. In particular, quoting Ayer, ‘the character of human nature is as constant as that of inanimate objects’. Therefore the idea of a social science is, for Hume, perfectly feasible, and in discussing morals, politics and religion he takes the approach of a social scientist rather than that of a moraliser himself.

After some brief and I think rather inconclusive discussion of freedom of the will, Ayer summarizes eleven main points which underlie Hume’s moral philosophy:-
1. ‘Reason’ is only concerned with the discovery of truth and falsehood. Therefore ‘reason’ can never in itself be the motive for any action of the will.
2. We are motivated by emotion (of one sort or another).
3. Sympathy for other creatures is a natural instinct.
4. Since morals influence our actions and affections, they cannot be derived from reason.
5. Moral judgments (such as ‘murder is wrong’) do not describe matters of fact. The description of an act is one thing; our feelings about it are quite another.
6. ‘Vice and virtue may be compared to sounds, colours, heat and cold which.... are not qualities in the object, but perceptions in the mind’.
7. Virtuous or vicious actions derive their merit or demerit only from virtuous or vicious motives.
8. What we call ‘virtuous’ arises from our own sentiments of approbation; likewise what we call vice is that which we find displeasing.
9. What arouses our approval or disapproval is what we perceive as causing pleasure or pain respectively. We characterize these appraisals as judgments of utility.
10. No action can be ‘good’ unless there is some motive to produce it [suggesting, it seems, that an action is not ‘good in itself’?].
11. Justice, on which both moral and political obligation depend, is derived not from nature but ‘artifice and human convention’.

I believe this list is a distillation, so to speak, produced by Ayer from Hume’s various writings, and I think it is helpful although as he says he does not attach any order of importance to the items in it. But in commenting on this list, I think I would rather (as elsewhere) make my own comments on Hume rather than simply reiterating those of Ayer.

For Hume, moral approval or disapproval are feelings. Words such as ‘good’, ‘bad’, ‘right’ or ‘wrong’ do not literally describe actions or events; they express our feelings about them. But Hume also said they are not merely words which betoken our personal likes or dislikes as do the words ‘nice’ or ‘nasty’; they are more than that. He emphasized that many of our feelings are in fact essential to the well-being of our fellow human beings and of society generally. These feelings include care and sympathy for others, generosity, aversion to cruelty for example, feelings without which human society would break down and become most disagreeable to everyone. Hume saw ‘being moral’, doing the right thing rather than the wrong thing, not as applying some abstract form of ‘moral knowledge’ or applying the precepts of a rigid moral code, but as feeling and behaving in a certain way.

Hume is also notable and important for having been the first philosopher ever to have identified and commented on the naturalistic fallacy which sometimes occurs within moral reasoning. Basically it is the elementary logical point that any argument of the form ‘x is the case, therefore x ought to be the case’ is invalid. Obviously we do not say ‘it is normal to be selfish, therefore we ought to be selfish’. This is a non-sequitur where the conclusion does not follow from the premise. But the same non-sequitur is found in less obvious examples such as ‘it is normal to procreate, therefore it is right to procreate’.
Hume said that further explanation is required if you want to establish a conclusion to the effect that x or y ought to be the case. So if you want to say ‘it is right, as a general rule, to procreate’ you can justify this by adding (for example) ‘otherwise there’d be no more people’ or something similar. There’s no need, in fact, to say that it’s ‘normal’, ‘natural’ (or ‘the will of God’) at all. The argument from ‘normality’ is fine in medical contexts (as in “your temperature is normal”), but in moral contexts it is misleading.

Hume also wrote on economics and politics. He was what you could call a small ‘c’ conservative, believing in respecting life and property, obeying the law, keeping promises, being fair, equitable and so on, otherwise society would not function without these modes of behaviour. Likewise he argued that human society ‘never could have place’, as he put it, were it not for the principles of justice. To put it in more modern terminology, as a ‘social scientist’ he saw ‘justice’ as a necessary condition for the functioning of society.

Hume did not write at any length on government (as did Locke) so he is not noted as a major ‘political philosopher’. He seemed to restrict himself to very general comments such as noting that government (of some sort) is necessary in human societies other than perhaps the most primitive. He observed that for all sorts of reasons government must depend to a greater or lesser extent upon the consent of the governed, but (quoting Ayer) ‘it does not follow from this that we have to invent a social contract as the moral justification for social obedience’. Hume therefore avoided the ‘philosophic fictions’, as Ayer called them, of social contracts. If pressed, I’m sure Hume would have criticized French philosopher Rousseau’s “Social Contract” as pure metaphor (maybe he did; I don’t know).

Hume’s political views more generally would have been fully consistent with those of the Scottish Enlightenment in the mid-eighteenth century, and he was a supporter of American independence. Of course, the ideological debates and conflicts between the political ‘left’ and the political ‘right’ lay in the future. We can only speculate what he would have made of Marxist ‘historical determinism’ or ‘dialectical materialism’. My guess is he would have regarded ideology as another species of metaphysics, nineteenth century metaphysics instead of mediaeval metaphysics, of course, but still metaphysics.

I think that as a person Hume would have been sympathetic to ideas of ‘natural rights’ or ‘human rights’, but wearing his philosopher’s hat I think he might have had reservations. Bearing in mind his views on religion, I think he would have been sceptical that ‘we are endowed by our Creator with inalienable rights’, as it says in the American Declaration of Independence. I don’t think he would have regarded such statements as ‘self-evident truths’ either, since for Hume there were very few self-evident truths about anything at all, other than tautologies. The sentence ‘we are endowed by our Creator with inalienable rights’ is not a tautology, therefore it cannot be a ‘self-evident truth’.

At the end of Chapter Five Ayer takes a very brief look at Hume’s views on religion. Firstly Hume denied there is any necessary connexion between morality and religion. As we have seen, he saw ethics and morality as modes of behaviour without which human society would not be viable, an empirical statement of fact which as such is logically independent of whether there is a deity or not.

But quite apart from the issue of morality, he saw no good reason for belief in a deity anyway, and in his Dialogues Concerning Natural Religion he rejected all the arguments in its support as either fallacious or lacking in foundation. A very good example is his refutation of the so-called ‘Argument from Design’, which Ayer summarizes.

Ayer concludes his book with one of the most famous quotations from Hume’s writings:-
“If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion.”

RHS, 2012