"Indulge your passion for science, says [Nature], but let your science be human, and such as may have a direct reference to action and society. Abstruse thought and profound researches I prohibit, and will severely punish, by the pensive melancholy which they introduce, by the endless uncertainty in which they involve you, and by the cold reception which your pretended discoveries shall meet with, when communicated. Be a philosopher; but amidst all your philosophy, be still a man."
(David Hume, Enquiry Concerning Human Understanding, 1748: p.5)
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David Hume was one of the greatest thinkers in Western history and certainly among the most delightful men to have ever graced a page with his pen. The eternally skeptical but always profound David Hume shook the edifice of Western thought to its very foundations - rousing the otherwise staid Immanuel Kant out of his "dogmatic slumber" to frantically attempt to rebuild it again. Over two centuries later, the rubble of the Humean earthquake - and its modern aftershocks - still lies awkwardly gazing at us from all corners of science and philosophy.
A Short Biography
Hume was more than a philosopher: he was also an accomplished historian, economist and sociologist - and, by all accounts, he was a really nice fellow too. David Hume presided over the "Scottish Enlightenment" (roughly dated from 1740 to 1790) which included Adam Smith, Francis Hutcheson, Adam Ferguson, Sir James Steuart, John Millar, Lord Kames, William Robertson and Thomas Reid - but it is safe to say that Hume's works outshine in insight, profundity and lasting value the combined output of all the others, indeed of all Europeans at the time. As his friend, Adam Smith put it, "I have always considered him, both in lifetime and since his death, as approaching as nearly to the idea of a perfectly wise and virtuous man, as perhaps the nature of human frailty will admit" (Smith, 1776).
Hume was certainly gifted - indeed, most of his ideas had been worked out by the time he was nineteen - but what Fortune bestows with one hand, it often takes away with the other. Born on April 26, 1711 in Edinburgh, Scotland, the second son of the lawyer Joseph Home and Katherine Falconer of Ninewells (an estate near Berwick-upon- Tweed). His father, a lawyer, died in 1713 and his mother raised him singlehandedly (Hume changed his name in 1731, when he perceived Englishmen having complications with the pronunciation of the Scottish "Home").
He enrolled at the university of Edinburgh in 1723 to study law (enrolling at twelve was not too astonishing in that century). However, philosophy and literature called and he withdrew from the university in 1729 and dedicated the next eight, long years, marred by illness, depression, frustration and mental breakdown, to the solitary study of that discipline and the construction of his formidable thesis - eventually laid out in his masterpiece A Treatise of Human Nature.
His project was complex enough: as the subtitle of his Treatise indicates, he sought to "introduce the experimental method of reasoning into moral subjects" - or, more simply, to introduce the scientific methods of the Enlightenment, of Newton and Bacon, to bear on five human subjects. These subjects were to be laid out in five volumes in the Treatise - I (Of the Understanding), II (Of the Passions), III (Of Morals), IV (Of Politics) and V (Of Criticism).
Seeking respite and restoration, David Hume went first to Bristol, England, to work for a sugar merchant but disappeared to France in 1734, settling down first at Rheims and then at La Flèche (near the celebrated Jesuit College of Anjou which Descartes had attended), where he set about writing the Treatise. Hume returned to Britain in 1737. Of the five volumes of the Treatise of Human Nature, only the first three were published in 1739 (Volumes I and II) and 1740 (Volume III). Hume was then twenty-nine years old.
The anonymously-published Treatise "fell deadborn from the press, without reaching such distinction as even to excite a murmur among the zealots" (Hume, 1776). This was not exactly true: the zealots disliked it and ensured that he was barred from academic appointments. An attempt to get a university chair at Edinburgh in 1745 was foiled by several clergymen and prominent townspeople who found him "subversive" - even after he had, in a fit of fright, pulled out his more contentious parts of his Treatise (such as the notorious essay on "Miracles") before publication.
Defeated, Hume became the tutor to the half-mad Marquis de Annandale and then later assistant to the restless General James St. Clair. With St. Clair, Hume ended up in Brittany as Judge Advocate, the bizarre outcome of a hare-brained military expedition originally intended for Canada. Hume followed St. Clair subsequently on embassies to Vienna and Turin. Returning to Edinburgh in 1751, another attempt at a university chair - this time at the University of Glasgow - failed again (reputedly, his timid friend, Adam Smith, could have done more for him there...).
Hume had originally envisaged the Treatise as a five-volume work. The first three, I (Of the Understanding), II (Of the Passions) and III (Of Morals), had appeared in 1739-40. The next two volumes, IV (Of Politics) and V (Of Criticism), never saw the light of day (although much of what he sought to write on these topics ended up in his later Essays). Hume concluded that the tepid, if not hostile, reception to the Treatise was due merely to his mode of presentation as opposed to its content. He re-worked the presentation of the arguments in the Treatise into more digestible forms via two "explanatory" tracts: an Abstract (1740) and A Letter from a Gentleman (1745), both directed to refuting the charges of the "zealots".
He continued working on other matters. Two collections of essays on various topics were published in the interim: Essays: Moral and Political (1742) and Three Essays (1748). These were, incidentally, the first publications to which he explicitly attached his name. In 1752, he published his Political Discourses, which contained most of his contributions to economics. These three collections of essays were eventually placed together in a single volume, Essays: Moral, Political and Literary in 1758. As it turns out, this was perhaps his best-received work.
At the tail-end of this period, Hume published two formidable enquiries, An Enquiry Concerning Human Understanding, (1748) and an Enquiry into the Principles of Morals (1751). The first clarified his epistemological theory, originally presented in Vol. I of the Treatise, in a clear and accessible manner (and took this opportunity to incorporate his discussion on "miracles"). The second enquiry did the same for his theory of ethics (which had been Vol. III of the Treatise). He considered this second work "incomparably the best" of all the works he had written.
In 1752, David Hume was appointed as librarian to the College of Advocates in Edinburgh. With so much time and resources about him, Hume set about writing his magnificent six-volume History of England (1754-1762). This work was not a new and independent interest of Hume's - rather, he saw it as a continuation of his other work, a "practical application" of his theses on politics. The Essays and the History of England restored much of the reputation he had lost with the Treatise and its aftermath.
But perhaps he got too cocky. In 1757, Hume published his Four Dissertations, which included the famous volume on The Natural History of Religion, lambasting Deistic "natural religion" (i.e. the then-popular idea that religion can be based on reason and not revelation), arguing instead that religious belief was very much a child of vulgar "superstition and enthusiasm". He was toying with fire now. He pressed on bravely, writing his highly atheistic Dialogues Concerning Natural Religion and two essays, "Of Suicide" and "Of the Immortality of the Soul". But sensing the trouble he was getting into, he suppressed these from publication.
In 1763, Hume returned left the library and returned to the world of men, accompanying the British ambassador to France, Lord Hertford, as personal secretary. Hume's reputation preceded him and he was the toast of enlightenment Paris. In 1766, he returned to London as Under- Secretary of State, bringing with him the much-persecuted Jean-Jacques Rousseau. Rousseau benefited tremendously from Hume's protection in England, writing his famous Letters from the Mountain against his critics from Hume's home. But Rousseau's paranoia and bitterness eventually tried even the eternal patience of the good-natured Hume. When they broke in 1767, Hume felt compelled by the swirling rumor-mills to write a tract explaining exactly the cause of their dispute.
In 1769, Hume left London for Edinburgh where he would remain until his death. There he lived in philosophical semi-retirement, correcting his earlier works, entertaining his fellow intellectuals of the Scottish Enlightenment and Mrs. Anne Ord. He wrote a short autobiographical notice, My Own Life in 1776, wherein he acknowledged, for the first time, his authorship of the Treatise. Despite a rather prolonged, painful illness, David Hume died on April 26, 1776, a happy, confirmed atheist until the end (for an account of Hume's last days, see Adam Smith's Letter to Strahan and James Boswell's Journal).
Before his death, he instructed Adam Smith to arrange for the publication of his long- suppressed two essays, "Of Suicide" and "Of the Immortality of the Soul" and his Dialogues Concerning Natural Religion. The ever-timid Smith refused to go through with it and so did his publisher William Strahan. Finally, his nephew published them in 1777, the Two Essays and the Dialogues appearing without the author's name nor even the publisher's.
Hume as Philosopher
Hume arrived unto philosophy with a simple query: what are the limits of human knowledge? - a question similar to the one posed many years later by Ludwig Wittgenstein. Thus, Kant would rightly call Hume the "geographer of human reason".
The question was not an empty one. The rationalists - from Descartes on - had claimed that the foundations of human knowledge are found in Reason - i.e. ideas innate in human nature. John Locke (1690) had questioned this assertion and concluded instead that knowledge was merely the complex combination of ideas that had been acquired through the senses. He got into a jam over relating objects to thought: Locke had argued that objects had "primary qualities" (e.g. extension,size, etc.) which impress themselves upon our senses; our mind then "reconstructs" these into secondary qualities (e.g. color, taste, sound, etc.) but that these secondary qualities are not necessarily "inherent" in the object. Thus, our knowledge consists merely of pictures of reality. They are not "innate" ideas, Locke argued, because these pictures are "generated" from outside.
George Berkeley's (1710) took the very simple step of refuting the division between qualities: our knowledge is not pictures of reality but pictures, period. They have no necessary connection to reality and merely exist in our head. Thus, Berkeley denied completely the material component of Locke's theory.
David Hume comes in here. He divided propositions between two types: those which are "relations of ideas" (analytic) and those which are "matters of fact" (synthetic). The first type are acquired without knowledge of anything in the world but solely from reasoning a priori; the second type are acquired only through experience.
"Relations of ideas" Hume confined to mathematics, geometry and pure logic. But he noted that they say nothing about reality because such statements are necessarily tautologies. "Relations of ideas" have several qualities - they do not need to be verified (e.g. one need not check that 2 + 2 = 4 is true, but just contemplate the meaning of "plus" and "equal"), they are true by definition (e.g. the definition of "four" is really "twice two"), negation leads to contradiction (e.g. if you say "sometimes 2 + 2 is not 4", you are contradicting the meaning of four) and, finally, they are "necessarily" true (its unimaginable that 2+2 could be anything else but four). But, Hume concludes, they are all tautologies (i.e. saying 2+2 or saying 4 is just repeating the same thing) and if they are all tautologies, they reveal nothing about reality. They are not even constructs of the human mind, but True by their very meaning - i.e. "2+2 = 4", "all bachelors are unmarried", "all triangles have three sides" are not meaningful propositions about the world but merely repeat in the predicate what they say in the subject.
What about "matters of fact"? These must be traced to particular sensations. What this means is that it must be imaginable as true and we know (more-or-less) which sensations we would have to experience to know it is true. Thus, the "sky is blue" is a "matter of fact" proposition, because we know what we would have to experience in our senses to conclude that the sky is blue.
However, if a proposition is neither a "relation of ideas" nor a "matter of fact", then they are not even propositions but mere "nonsense" (to use Wittgenstein's term). Therefore, metaphysical claims like the existence of God are all outside human knowledge and become "belief", i.e. ideas which do not arise from experience and are not true a priori. "God exists" is not an relation of ideas: denying it doesn't make create a contradiction ("God does not exist" does not contradict the concept of God), it is not true by definition ("God" and "existence" are not the same), it is not "necessarily" true (we can imagine God not existing), it is not a priori (i.e. we cannot ascertain God's existence by merely contemplating the meaning of that statement). Thus, the proposition that "God exists" is certainly not a tautology and therefore is not a "relation of ideas".
But can it be related to "matters of fact"? What possible sensible experience could easily lead to the conclusion that God exists? Traditional answers are of two sorts: one, we have the experience of "miracles". But there is no necessary connection there: a "burning bush" or a blind man who is cured are not necessarily imply belief in God's existence. A burning bush can (and have) led to beliefs in the existence of lightning, St. Elmos fire, Vulcan, etc. and not necessarily God. Thus the concept of God's existence cannot be predicated on such presumed "demonstrations" because there is not a clear set of sense-perceptions which would demonstrate that proposition.
A second avenue is to follow the realm of causation. We have, it is claimed, the experience of "causation", and if "causation" is true, then there must be a "First Cause" - and let us therefore call it God. This is a common argument in "Natural Religion". Here Hume makes his famous attack on causation.
Hume's position was simply this: causation itself is not an meaningful proposition. Or rather, "causation" itself is not a "relation of ideas" (e.g. the negation of the statement "rising sun causes the rooster to crow" when negated does not provide a contradiction). Furthermore, it also cannot be traced back to particular sensations, thus it is not a "matter of fact" either. We have no "necessary connnection" between the sense data and the proposition of causation: we see merely one thing happening and the other thing following and therefore we often presume (without knowing), that one is causing the other, but it is perfecly possible not to presume it. In his famous billiard ball example, Hume argues this beautifully.
Causation, in Hume's argument, is thus merely a habit of association, a "belief" every bit as unfounded and meaningless. As he writes in his Enquiry:
"When we look about us towards external objects, and consider the operation of causes, we are never able, in a single instance, to discover any power or necessary connexion...We only find, that the one does actually, in fact, follow the other."
(D. Hume, 1748: p.67)
and then goes on to note that:
"But when one particular species of event has always, in all instances, been conjoined with another, we make no longer any scruple of foretelling one upon the appearance of the other...We then call that one object, Cause; the other, Effect. We suppose that there is some connextion between them; some power in the one, by which it infallibly produces the other, and operates with the greatest certainty and strongest necessity."
(D. Hume, 1748: p.80-81)
But Hume cautioned that this was misleading. Does the crowing cock "cause" the sun to rise? Historically speaking, his crowing immediately precedes sunrise and so is a very consistent predictor, yet would one consider a causal relation to have been found? Nonsense. The first time one sees this, they are merely "conjoined" events; but as it repeats itself over time, imagination takes over and we begin to ascribe a "connection" - but this, as Hume notes, is only a human "feeling", that when we say X causes Y "we mean only that they have acquired a connexion in our thought and give rise to this inference [of causation]." (p.82), but the truth of the matter, our sense perceptions only tell us "X tends to happen first, Y tends to happen after"
Already we are reaching into the realm of probability - another point on which Hume makes a contribution. A lot of science, after all, tends to rely on the concept of causation: e.g. heat causes metals to expand. But we have no certainty of causation in this, but only the conjoined events. Therefore, the meaning of "causation" becomes simply that: "every time I heat a metal, it tends to be followed by expansion". Thus, nothing is certain to follow something else, only "probable". Hume's redefinition of scientific "causation" as mere "probability" in linking events fits quite well in the post-Quantum age. Already early in this century, many scientists such as Max Planck went to great lengths to recast the scientific meaning of causation and determinism in probabilistic terms.
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