The Scottish philosopher David Hume (1711-1776) developed a philosophy of "mitigated skepticism," which remains a viable alternative to the systems of rationalism, empiricism, and idealism.
If one was to judge a philosopher by a gauge of relevance—the quantity of issues and arguments raised by him that remain central to contemporary thought— David Hume would be rated among the most important figures in philosophy. Ironically, his philosophical writings went unnoticed during his lifetime, and the considerable fame he achieved derived from his work as an essayist and historian. Immanuel Kant's acknowledgment that Hume roused him from his "dogmatic slumbers" stimulated interest in Hume's thought.
With respect to Hume's life there is no better source than the succinct autobiography, My Own Life, written 4 months before his death. He was born on April 26, 1711, on the family estate, Ninewells, near Edinburgh. According to Hume, the "ruling passion" of his life was literature, and thus his story contains "little more than the History of my writings." As a second son, he was not entitled to a large inheritance, and he failed in two family-sponsored careers in law and business because of his "unsurmountable aversion to everything but the pursuits of Philosophy and general learning." Until he was past 40, Hume was employed only twice. He spent a year in England as a tutor to a mentally ill nobleman, and from 1745 to 1747 Hume was an officer and aide-de-camp to Gen. James Sinclair and attended him on an expedition to the coast of France and military embassies in Vienna and Turin.
During an earlier stay in France (1734-1737) Hume had written his major philosophic work, A Treatise of Human Nature. The first two volumes were published in 1739 and the third appeared in the following year. The critical reception of the work was singularly unfortunate. In Hume's own words, the Treatise "fell dead born from the press." Book I of the Treatise was recast as An Enquiry concerning Human Understanding and published in 1748. The third volume with minor revisions appeared in 1751 as An Enquiry concerning the Principles of Morals. The second volume of the Treatise was republished as Part 2 of Four Dissertations in 1757. Two sections of this work dealing with liberty and necessity had been incorporated in the first Enquiry. Hume's other important work, Dialogues concerning Natural Religion, was substantially complete by the mid-1750s, but because of its controversial nature it was published posthumously.
During his lifetime Hume's reputation derived from the publication of his Political Discourses (1751) and six-volume History of England (1754-1762). When he went to France in 1763 as secretary to the English ambassador, Hume discovered that he was a literary celebrity and a revered figure among the philosophes. He led a very happy and active social life even after his retirement to Edinburgh in 1769. He died there on Aug. 25, 1776. He specified in his will that the gravestone be marked only with his name and dates, "leaving it to Posterity to add the rest."
Skepticism is concerned with the truthfulness of human perceptions and ideas. On the level of perception, Hume was the first thinker to consistently point out the disastrous implications of the "representative theory of perception," which he had inherited from both his rationalist and empiricist predecessors. According to this view, when I say that I perceive something such as an elephant, what I actually mean is that I have in my mind a mental idea or image or impression. Such a datum is an internal, mental, subjective representation of something that I assume to be an external, physical, objective fact. But there are, at least, two difficulties inherent in ascribing any truth to such perceptions. If truth is understood as the conformity or adequacy between the image and the object, then it is impossible to establish that there is a true world of objects since the only evidence I have of an external world consists of internal images. Further, it is impossible to judge how faithfully mental impressions or ideas represent physical objects.
Hume is aware, however, that this sort of skepticism with regard to the senses does violence to common sense. He suggests that a position of complete skepticism is neither serious nor useful. Academic skepticism (the name derives from a late branch of Plato's school) states that one can never know the truth or falsity of any statement (except, of course, this one). It is, however, a self-refuting theory and is confounded by life itself because "we make inferences on the basis of our impressions whether they be true or false, real or imaginary." Total skepticism is unlivable since "nature is always too strong for principle." Hume therefore advances what he calls "mitigated skepticism." In addition to the exercise of caution in reasoning, this approach attempts to limit philosophical inquiries to topics that are adapted to the capacities of human intelligence. It thus excludes all metaphysical questions concerning the origin of either mind or object as being incapable of demonstration.
Theory of Knowledge
Even though an ultimate explanation of both the subject or object of knowledge is impossible, Hume provides a description of how man senses and understands. He emphasizes the utility of knowledge as opposed to its correctness and suggests that experience begins with feeling rather than thought. He uses the term "perception" in its traditional sense—that is, whatever can be present to the mind from the senses, passions, thought, or reflection. Nonetheless he distinguishes between impressions which are felt and ideas which are thought. In this he stresses the difference between feeling a toothache and thinking about such a pain, which had been obscured by both rationalists and empiricists. Both impressions and ideas are subdivided further into simple and complex; for example, the idea of heat is simple, while the idea of combustion is complex.
These simple divisions are the basis for Hume's "phenomenalism" (that is, knowledge consists of "appearances" in the mind). Hume distinguishes the various operations of the mind in a descriptive psychology, or "mental geography." Impressions are described as vivacious and lively, whereas ideas are less vivid and, in fact, derived from original impressions. This thesis leads to the conclusion that "we can never think of any thing which we have not seen without us or felt in our own minds." Hume often overestimates the importance of this discovery with the suggestion that the sole criterion for judging ideas is to remove every philosophical ambiguity by asking "from what impression is that supposed idea derived." If there is no corresponding impression, the idea may be dismissed as meaningless. This assumption that all ideas are reducible, in principle, to some impression is a primary commitment of Hume's empiricism. Hume did admit that there are complex ideas, such as the idea of a city, that are not traceable to any single impression. These complex ideas are produced by the freedom of the imagination to transform and relate ideas independently of impressions; such ideas are not susceptible to empirical verification. This represents the major paradox of Hume's philosophy—the imagination which produces every idea beyond sensible immediacy also denies the truth of ideas.
Theory of Ideas
Hume accepts the Cartesian doctrine of the distinct idea—conceivability subject only to the principle of contradiction—as both the unit of reasoning and the criterion of truth. But the doctrine of the distinct idea means that every noncontradictory idea expresses an a priori logical possibility. And the speculative freedom of the imagination to conceive opposites without contradiction makes it impossible to demonstrate any matter of fact or existence. This argument leads to a distinction between relations of ideas (demonstrations which are true a priori) and matters of fact (the opposite of which is distinctly conceivable). And this distinction excludes from the domain of rational determination every factual event, future contingent proposition, and causal relation. For Hume, since truth is posterior to fact, the ideas of reason only express what the mind thinks about reality.
Distinct ideas, or imaginative concepts, are pure antinomies apart from experience as every factual proposition is equally valid a priori. But Hume does acknowledge that such propositions are not equally meaningful either to thought or action. On the level of ideas, Hume offers a conceptual correlative to the exemption of sensation as a form of cognition by his recognition that the meaning of ideas is more important than their truth. What separates meaningful propositions from mere concepts is the subjective impression of belief.
Belief, or the vivacity with which the mind conceives certain ideas and associations, results from the reciprocal relationship between experience and imagination. The cumulative experience of the past and present—for example, the relational factors of constancy, conjunction, and resemblance—gives a bias to the imagination. But it is man's imaginative anticipations of the future that give meaning to his experience. Neither the relational elements of experience nor the propensive function of the imagination, from the viewpoint of the criterion of truth, possesses the slightest rational justification. Hence the interplay between the criterion of truth and the logic of the imagination explains both Hume's skepticism and his conception of sensation and intellection.
The most celebrated example of this argument is Hume's analysis of the causal relation. Every statement which points beyond what is immediately available to the senses and memory rests on an assumption and/or extension of the cause and effect relation. Let us examine two cases: I see lightning and hear thunder; I see a rabbit and then a fox. The question is why I am right in concluding that lightning causes thunder but wrong in believing that rabbits cause foxes. Experience, in both instances, reveals an A that is followed by B, and repeated experiences show that A is always followed by B. While the constant conjunction of A and B might eliminate the rabbit-fox hypothesis, it is of no help in explaining causality because there are all sorts of objects, such as tables and chairs, which are similarly conjoined but not supposed to be causally related. Thus experience reveals only that constant conjunction and priority are sufficient but not necessary conditions for establishing a causal connection. And it is necessity, understood as that which cannot be otherwise than it is, which makes a relation causal in the propositional form of "If A then B must appear and if no A then no B."
But if necessary connection explains causality, what explains necessity? Experience yields only a particular instance and tells us nothing about the past or the future. Nor is there any necessity discoverable in repeated experiences. That the sun will rise tomorrow because it has in the past is an assumption that the past necessarily causes the future which is, of course, the connection that is to be demonstrated. If experience cannot account for necessity, then reason fares no better. I can always imagine the opposite of any matter of fact without contradiction. If someone tells me that Caesar died of old age or that thunder is uncaused or that the sun will not rise tomorrow, I will not believe him, but there is nothing logically incorrect about such statements since for every probability "there exists an equal and opposite possibility." Thus there is no justifiable knowledge of causal connections in nature, although this is not a denial that there are real causes. Man's supposed knowledge results from repeated associations of A and B to the point where the imagination makes its customary transition from one object to its usual attendant, that is, "an object followed by another, and whose appearance always conveys the thought to that other."
Because of his skeptical attitude toward the truths of reason Hume attempted to ground his moral theory on the bedrock of feeling—"Reason is, and ought only to be, the slave of the passions." In this, Hume followed the "moral sense" school and, especially, the thought of Francis Hutcheson. The notion that virtue and vice are to be derived ultimately from impressions of approbation and blame or pleasure and pain shows that Hume anticipated Jeremy Bentham's utilitarianism, a debt which the latter acknowledged. Although Hume considered himself to be primarily a moralist, this doctrine is the least original part of his philosophical writings.
Further Reading on David Hume
Ernest C. Mossner, who edited several volumes of Hume's correspondence, also wrote the best biography, The Life of David Hume (1954). John H. Burton, Life and Correspondence of David Hume (1846; repr. 1967), is still useful. Good studies of Hume include John A. Passmore, Hume's Intentions (1952); Farhang Zabeeh, Hume, Precursor of Modern Empiricism (1960); and Charles W. Hendel, Studies in the Philosophy of David Hume (1963). Also useful are Alfred B. Glathe, Hume's Theory of the Passions and of Morals (1950); and Antony Flew, Hume's Philosophy of Belief (1961), a study of the first Enquiry. Various aspects of Hume's work are considered in several anthologies of critical opinion: D. F. Pears, ed., David Hume: A Symposium (1963); Alexander Sesonske and Noel Fleming, eds., Human Understanding: Studies in the Philosophy of David Hume (1965); and V. C. Chappell, ed., Hume (1966).