David Hume (1711-1776) was a Scottish philosopher and historian who was born in Edinburgh. He studied at the University of Edinburgh, but his application for a professorship there was rejected because of opposition by the local clergy to the allegedly atheistic views that he had expressed in his A Treatise of Human Nature (1739-1740). He was appointed librarian of the Advocates' Library in 1772, and he then served as Secretary at the British embassy in Paris (1763-1765) and as Undersecretary of State at the Home Office in London (1767-1768). He returned to Edinburgh in 1768, and he died there is 1776. His other major writings included Essays Moral and Political (1741-1742), An Enquiry Concerning Human Understanding (1748), An Enquiry Concerning the Principles of Morals (1751), The History of England (1754-1762), and Dialogues Concerning Natural Religion (1779). A Treatise of Human Nature (1739) is an investigation of the origin, nature, and limits of human knowledge. Hume divides acts of understanding into two kinds: (1) comparisons of ideas, and (2) inferences concerning matters of fact. In his view, all knowledge is based upon these two kinds of reasoning, and the most important relation with which understanding is concerned is the relation of cause and effect.
All ideas are originally derived from sensory perceptions, says Hume, and knowledge is ultimately based on experience rather than reason. In order to establish the existence of an object, we must either have had a sensory perception of that object or have had a sensory perception of other objects from which the existence of that object can be inferred. Reason alone is insufficient to establish the existence of an object. Sensory perception of an object, directly or indirectly, is necessary in order to prove the existence of that object. Thus, the idea of the existence of an object is the same as having the idea of the object itself.
Reason alone is insufficient to motivate human action, says Hume. Reason must excite passion and emotion if it is to have any influence on the motives or actions of the will. Reason can prevent the expression of a passion or emotion only by exciting a contrary passion or emotion. However, reason and passion are not necessarily contradictory to each other. Reason may promote the expression of passion rather than prevent or suppress it. It may allow passion to provide a motivating force for moral conduct. Passion and reason are not contradictory to each other, unless passion is caused by a false perception of reality or is expressed in a manner that is contradictory to its own aim. Indeed, if reason is to influence moral conduct, reason must either excite a passion for a proper object or reveal how a passion for a proper object may be expressed.
The Treatise is divided into three volumes or books. Book I is entitled "Of the Understanding," Book II is entitled "Of the Passions," and Book III is entitled "Of Morals." Book I is concerned with the origin of ideas, with the distinction between simple and complex ideas, the kinds of relations which may occur between ideas, and with the nature and causes of belief. Book II is concerned with the causes of the passions, the objects and aims of the passions, the influence of reason on the passions, and the nature of human liberty and necessity. Book III provides an explanation of how moral distinctions may arise from differences between the feelings of pleasure and pain, and it considers the importance of sympathy as a principle of moral conduct.
According to Hume, perceptions may be of two kinds: impressions, and ideas. Impressions include sensations, passions, and emotions. Sensations are primary or original impressions, while passions and emotions are secondary or reflective impressions. Secondary impressions may be derived from primary impressions, and secondary ideas may be derived from primary ideas. Primary ideas are mental images of sensory impressions. The only difference between ideas and impressions is that ideas are "weaker" or "less lively" perceptions, while impressions are "stronger" or "more lively" perceptions.1
Perceptions may be simple or complex. Simple perceptions are indivisible, but complex perceptions are divisible. Complex impressions may be derived from simple impressions, and complex ideas may be derived from simple ideas. Simple impressions are the original source of all simple ideas. Every simple idea corresponds to an original simple impression. Primary ideas are mental images of impressions, and secondary ideas are mental images of primary ideas.
There are no innate ideas in the human mind, says Hume, because all ideas are originally derived from impressions. In order for ideas to appear in the mind, there must originally have been some sensory impressions to produce them.
There are three kinds of connections or associations that may occur between ideas: (1) resemblance, (2) contiguity in time or place, and (3) causation. These connections or associations of ideas are mental processes or operations by which simple ideas may be combined into complex ideas such as relations, modes, and substances.
According to Hume, seven kinds of relations may occur between objects: (1) resemblance, (2) identity, (3) space and time, (4) quantity or number, (5) quality or degree, (6) contrariety, and (7) cause or effect. Relations, modes, and substances may be combinations of simple ideas that are assembled in variable order and form by the imagination in order to try to explain the true nature of reality.
Our ideas of time and space are composed of indivisible parts, says Hume. If our ideas of time and space were not composed of indivisible parts, then it would be possible for them to be infinitely divisible, and if they were adequate representations of the properties of time and space, then time and space would also be infinitely divisible. If time and space were infinitely divisible, then a moment in time or a position in space could be divided into an infinite number of coexisting moments in time or positions in space, and those coexisting moments or positions would be indistinguishable from each other. Thus, our experience of time consists of a succession of distinct moments, and our experience of space consists of a compound impression of distinct sensations.
Depending on how closely our ideas correspond to sensory or reflective impressions, they may vary as to their degree of clarity or obscurity, and distinctness or indistinctness. Thus secondary ideas that are produced by remembering original impressions are "stronger" and "livelier" than those that are produced by the imagination. Moreover, recent memories are more likely to be "strong" and "lively" than remote memories. As memories become more remote, they lose their "strength" and "vivacity," and they are more likely to be influenced by the imagination.
A belief is a lively idea that is associated with a present impression.2 The influence of a belief on other ideas or feelings may be determined by its strength and vivacity. The greater the strength and vivacity of an idea, the greater the influence it may have on other ideas or feelings. The strength and vivacity of an idea may be determined by how closely it corresponds to the original impression from which it is derived.
Hume describes the idea of cause and effect as a fundamental aspect of our reasoning about matters of fact. The idea of cause and effect may be based on ideas about four kinds of relations: (1) contiguity in time or place (the finding that a cause and an effect are contiguous in time or place), (2) temporal precedence (the finding that a cause always occurs prior to an effect), (3) constant conjunction (the finding that a cause and an effect always occur in regular succession), and (4) necessary connection (the finding that a cause and an effect are necessarily connected with each other).
However, Hume says that since every idea of which the mind is capable must originally be derived from a sensory impression, there cannot be any idea of a necessary connection between a cause and an effect unless there is a corresponding impression from which this idea may be derived. Since we cannot have any sensory impression of a necessary connection between a cause and an effect, the only cause and effect relations that we can confirm by experience are those of contiguity in time or place, temporal precedence, and constant conjunction. Thus, the idea of a necessary connection between a cause and an effect may be derived from an impression of reflection, and it may only be a representation of an internal impression that does not correspond to any external reality.
We cannot prove that there is a necessary connection between a cause and an effect or between an impression and a corresponding idea. Thus, we cannot prove that any causal relation between constantly conjoined or regularly successive events is logically necessary. We cannot prove that there is a necessary connection between our perceptions and reality. Moreover, we cannot prove the existence of an objective world beyond that which is capable of being experienced by sensory perception.
Hume’s skepticism applies to his approach to metaphysical and religious questions as well. For example, he declares that we cannot prove that the universe is necessarily created by God. If we cannot prove that there is any necessary connection between God and the creation of the universe, then we can only try to confirm by experience that the universe and God are constantly conjoined.
Hume disagrees with the Aristotelian principle that there are four kinds of causes (formal, material, efficient, and final), arguing instead that every cause is efficient insofar as the idea of efficiency has its source in the impression of a constant conjunction of a cause and an effect. There is only one kind of necessity, he says, and there is no difference between moral and physical necessity. Necessity is a constant conjunction of objects, this conjunction occurring so regularly and invariably that the idea of one of the objects determines the mind to form the idea of the other object or objects.3
Secondary impressions may be produced by primary impressions (or ideas), and they may be divided into two kinds: calm (ideas of reflection) and violent (passions and emotions). Passions may also be divided into two kinds: direct and indirect. Passions that arise directly from the sensations of pleasure or pain include desire, aversion, grief, joy, hope, and despair. Passions that arise indirectly from the sensations of pleasure or pain include pride, humility, ambition, vanity, love, hatred, envy, pity, malice, and generosity.3
Our actions are determined by our passions and not by our powers of reason, says Hume. Our passions may be excited or quieted by our powers of reason, but reason alone is insufficient to cause or prevent any form of action. The difference between good and evil is not discoverable by reason; it arises from the difference between agreeable and disagreeable impressions or from the difference between pleasure and pain.
Thus, the moral quality of an action is determined by the motives and not by the consequences of that action. Actions cannot be virtuous unless their motives are virtuous. Virtuous actions cannot be motivated by malevolent or intemperate passions. Every action is motivated by passion, which is the source of its moral quality. Some passions may motivate virtuous actions, while others may motivate non-virtuous actions. The moral quality of an action is determined by whether pleasure or pain is the source of the passion that motivates the action.
There is no sensory impression that can be the source of the idea of a self as a complex system of ideas, says Hume, and there is no simple impression from which every idea about the identity of a self may be derived. The self is nothing but a bundle of perceptions, and no impression can be attained of the self other than that of a collection of changing perceptions.
Hume emphasizes the importance of sympathy as a principle of human nature, and he says that sympathy may be a source of moral virtue. Sympathy may enable us to express concern for others, and it may help us to be more aware of the feelings of others. It may also be an important factor in the development of moral understanding, and it may produce a desire to promote the harmony and well-being of society.
1David Hume, A Treatise of Human Nature, edited by Ernest C. Mossner (London, Penguin Books, 1969), p. 49.
2Ibid., p. 144.
3Ibid., p. 221-2.
4Ibid., p. 328.
Hume, David. A Treatise of Human Nature. Edited by Ernest C. Mossner. London: Penguin Books, 1969.