David (1711–76), Scottish philosopher and historian who may be aptly considered the leading neo-skeptic of the early modern period. Many of Hume’s immediate predecessors (Descartes, Bayle, and Berkeley) had grappled with important elements of skepticism. Hume consciously incorporated many of these same elements into a philosophical system that manages to be both skeptical and constructive. Born and educated in Edinburgh, Hume spent three years (1734–37) in France writing the penultimate draft of A Treatise of Human Nature. In middle life, in addition to writing a wide-ranging set of essays and short treatises and a long History of England, he served briefly as companion to a mad nobleman, then as a military attaché, before becoming librarian of the Advocates Library in Edinburgh. In 1763 he served as private secretary to Lord Hertford, the British ambassador in Paris; in 1765 he became secretary to the embassy there and then served as chargé d’affaires. In 1767–68 he served in London as under-secretary of state for the Northern Department. He retired to Edinburgh in 1769 and died there.
Hume’s early care was chiefly in the hands of his widowed mother, who reported that young David was ‘uncommon wake-minded’ (i.e., uncommonly acute, in the local dialect of the period). His earliest surviving letter, written in 1727, indicates that even at sixteen he was engaged in the study that resulted in the publication (1739) of the first two volumes of A Treatise of Human Nature. By the time he left college (c.1726) he had a thorough grounding in classical authors, especially Cicero and the major Latin poets; in natural philosophy (particularly that of Boyle) and mathematics; in logic or theory of knowledge, metaphysics, and moral philosophy; and in history. His early reading included many of the major English and French poets and essayists of the period. He reports that in the three years ending about March 1734, he read ‘most of the celebrated Books in Latin, French & English,’ and also learned Italian. Thus, although Hume’s views are often supposed to result from his engagement with only one or two philosophers (with either Locke and Berkeley, or Hutcheson or Newton), the breadth of his reading suggests that no single writer or philosophical tradition provides the comprehensive key to his thought.
Hume’s most often cited works include A Treatise of Human Nature (three volumes, 1739–40); an Abstract (1740) of volumes 1 and 2 of the Treatise; a collection of approximately forty essays (Essays Moral, Political, and Literary, first published, for the most part, between 1741 and 1752); An Enquiry concerning Human Understanding (1748); An Enquiry concerning the Principles of Morals (1751); The Natural History of Religion (1757); a six-volume History of England from Roman times to 1688 (1754–62); a brief autobiography, My Own Life (1777); and Dialogues concerning Natural Religion (1778).
Hume’s neo-skeptical stance manifests itself in each of these works. He insists that philosophy ‘cannot go beyond experience; and any hypothesis, that pretends to discover the ultimate original qualities of human nature, ought at first to be rejected as presumptuous and chimerical.’ He says of the Treatise that it ‘is very sceptical, and tends to give us a notion of the imperfections and narrow limits of the human understanding.’ But he goes well beyond the conventional recognition of human limitations; from his skeptical starting place he projects an observationally based science of human nature, and produces a comprehensive and constructive account of human nature and experience. Hume begins the Treatise with a discussion of the ‘elements’ of his philosophy. Arguing that it is natural philosophers (scientists) who should explain how sensation works, he focuses on those entities that are the immediate and only objects present to the mind. These he calls ‘perceptions’ and distinguishes into two kinds, ‘impressions’ and ‘ideas.’ Hume initially suggests that impressions (of which there are two kinds: of sensation and of reflection) are more forceful or vivacious than ideas, but some ideas (those of memory, e.g.) do sometimes take on enough force and vivacity to be called impressions, and belief also adds sufficient force and vivacity to ideas to make them practically indistinguishable from impressions. In the end we find that impressions are clearly distinguished from ideas only insofar as ideas are always causally dependent on impressions. Thomas Reid charged that the allegedly representative theory of perception found in Descartes and Locke had served as a philosophical Trojan horse leading directly to skeptical despair. Hume was fully aware of the skeptical implications of this theory. He knew well those sections of Bayle and Locke that reveal the inadequacy of Descartes’s attempts to prove that there is an external world, and also appreciated the force of the objections brought by Bayle and Berkeley against the primary–secondary quality distinction championed by Locke. Hume adopted the view that the immediate objects of the mind are always ‘perceptions’ because he thought it correct, and in spite of the fact that it leads to skepticism about the external world. Satisfied that the battle to establish absolutely reliable links between thought and reality had been fought and lost, Hume made no attempt to explain how our impressions of sensation are linked to their entirely ‘unknown causes.’ He instead focused exclusively on perceptions qua objects of mind: As to those impressions, which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and ’twill always be impossible to decide with certainty, whether they arise immediately from the object, or are produc’d by the creative power of the mind, or are deriv’d from the author of our being. Nor is such a question any way material to our present purpose. We may draw inferences from the coherence of our perceptions, whether they be true or false; whether they represent nature justly, or be mere illusions of the senses. Book I of the Treatise is an effort to show how our perceptions cohere to form certain fundamental notions (those of space and time, causal connection, external and independent existence, and mind) in which, skeptical doubts notwithstanding, we repose belief and on which ‘life and action entirely depend.’
According to Hume, we have no direct impressions of space and time, and yet the ideas of space and time are essential to our existence. This he explains by tracing our idea of space to a ‘manner of appearance’: by means of two senses, sight and touch, we have impressions that array themselves as so many points on a contrasting background; the imagination transforms these particulars of experience into a ‘compound impression, which represents extension’ or the abstract idea of space itself. Our idea of time is, mutatis mutandis, accounted for in the same way: ‘As ’tis from the disposition of visible and tangible objects we receive the idea of space, so from the succession of ideas and impressions we form the idea of time.’ The abstract idea of time, like all other abstract ideas, is represented in the imagination by a ‘particular individual idea of a determinate quantity and quality’ joined to a term, ‘time’, that has general reference.
Hume is often credited with denying there is physical necessity and that we have any idea of necessary connection. This interpretation significantly distorts his intent. Hume was convinced by the Cartesians, and especially by Malebranche, that neither the senses nor reason can establish that one object (a cause) is connected together with another object (an effect) in such a way that the presence of the one entails the existence of the other. Experience reveals only that objects thought to be causally related are contiguous in time and space, that the cause is prior to the effect, and that similar objects have been constantly associated in this way. These are the defining, perceptible features of the causal relation. And yet there seems to be more to the matter. ‘There is,’ he says, a ‘NECESSARY CON- NECTION to be taken into consideration,’ and our belief in that relation must be explained. Despite our demonstrated inability to see or prove that there are necessary causal connections, we continue to think and act as if we had knowledge of them. We act, for example, as though the future will necessarily resemble the past, and ‘wou’d appear ridiculous’ if we were to say ‘that ’tis only probable the sun will rise to-morrow, or that all men must dye.’ To explain this phenomenon Hume asks us to imagine what life would have been like for Adam, suddenly brought to life in the midst of the world. Adam would have been unable to make even the simplest predictions about the future behavior of objects. He would not have been able to predict that one moving billiard ball, striking a second, would cause the second to move. And yet we, endowed with the same faculties, can not only make, but are unable to resist making, this and countless other such predictions. What is the difference between ourselves and this putative Adam? Experience. We have experienced the constant conjunction (the invariant succession of paired objects or events) of particular causes and effects and, although our experience never includes even a glimpse of a causal connection, it does arouse in us an expectation that a particular event (a ’cause’) will be followed by another event (an ‘effect’) previously and constantly associated with it. Regularities of experience give rise to these feelings, and thus determine the mind to transfer its attention from a present impression to the idea of an absent but associated object. The idea of necessary connection is copied from these feelings. The idea has its foundation in the mind and is projected onto the world, but