David Hume

David Hume (7 May 1711 – 25 August 1776) was a Scottish philosopher, historian, and essayist; he is widely considered the most important philosopher to write in the English language. Hume’s contributions to our understanding of scientific knowledge and scientific change come from his major philosophical works including A Treatise of Human Nature (1738) and Enquiries concerning Human Understanding (1748). He is most noted for his skeptical views on a variety of topics including the powers of human reason, metaphysics, human identity, and the existence of God.1 He is perhaps best known, first, for rejecting Aristotle’s epistemological distinction between knowledge and belief and replacing it with his own distinction between matters of fact (which depend on the way the world is) and relations of ideas (that are discoverable by thought, such as mathematical truths). This new distinction is known as Hume's Fork. Secondly, he is known for questioning the justifiability of knowledge derived from inductive reasoning. The problem he posed is known as Hume's Problem of Induction. 2 The impact of these skeptical arguments is still felt to this day.

Historical Context

David Hume was born in Edinburgh, Scotland in 1711. His family had a modest estate and was socially connected, but not wealthy.3 They recognized that Hume was precocious, and sent him to Edinburgh University two years early (at the age of 10 or 11) with his older brother (who was 12). He studied Latin and Greek, read widely in history, literature, and ancient and modern philosophy, as well as some mathematics and natural philosophy. 24p. 35-65 Both at home and at the university, Hume was raised in the stern Calvinist faith, with prayers and sermons as prominent features of his home and university life. 2 Following the completion of his studies, Hume rejected his family's plan that he become a lawyer, and instead determined to become a scholar and philosopher, engaging in three years of intensive personal study. Living in the aftermath of the acceptance of Isaac Newton's(1643-1727) revolutionary theories of motion and gravitation, eighteenth century thinkers proclaimed the 'Age of Enlightenment' and expected philosophy (which then included what we would call the natural and social sciences) to dramatically improve human life. 5 Hume, like many of his times, revered Newton, calling him "the greatest and rarest genius that ever arose for the ornament and instruction of the species". 6

Although little is known of Hume's activities during his schooling and afterwards, he would have spent the fourth year of the curriculum at Edinburgh studying natural philosophy, and would have been exposed to experimental natural philosophy, including Newton's theories. 4p. 38-40 More than thirty years earlier, in 1687, Newton had published his Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) in which he put forth his laws of motion, law of universal gravitation, and his inductive experimental philosophy. 78 By about 1700 these theories had become accepted in Britain. 9p. 210 The works of other experimental philosophers were also available to the young Hume. The natural philosophy library at Edinburgh, to which Hume is known to have contributed, contained an extensive collection of the works of Robert Boyle(1627-1691), the works of Rene Descartes (1596-1650), and John Locke's (1632-1704) Essay Concerning Human Understanding. This work, published in 1689, more than twenty years before Hume was born, propounded Locke's empiricist view of human knowledge. 4p. 38-4010 Boyle, Newton, and Locke were all associated with the Royal Society of London, which was founded in 1663, almost 50 years before Hume's birth, and sought to promote the experimental method and the new natural philosophy. 1011

By Hume's time, Aristotle's (384 BC-322 BC) teleological account of causation had been rejected in favour of the corpuscular mechanistic view of causation. Derived from ancient atomism, it held that material bodies are made of invisibly small particles, called corpuscles. The only form of causation is mechanical, by direct physical contact of bodies or their constituent corpuscles. 6 Natural philosophers continued to accept Aristotle's distinction between scientific knowledge and belief. Scientific knowledge was taken to be knowledge of causes and consisted of demonstrations; proving the necessary connection between cause and effect. Locke supported this view of knowledge and made the popular notion of a hypothetical hidden corpuscular microstructure and the associated notion of a metaphysically necessary connection between cause and effect central to his system. He nonetheless viewed demonstrative knowledge as seldom attainable because of the unobservability of corpuscles. 612

Although many early eighteenth century thinkers regarded Newton's theories and Locke's empiricism to constitute a unified system, there was a distinct tension between them, which Hume recognized. Newton had been unable to explain his gravitational force in terms of a corpuscular mechanism. He saw his inductive method as an alternative to the demands of a corpuscularism that stood in the way of the acceptance of a mathematically lawful gravitational force on its own terms. Hume's Newton inspired skepticism of speculative metaphysical hypotheses led him to reject corpuscularism, and his enthusiastic championing of Newton's inductive method led him to challenge Locke's concept of causation, and Aristotle's taxonomy of knowledge and opinion in favour of a new epistemic taxonomy and new concept of causation. 132

By the time he started work on A Treatise of Human Nature at the age of 23, Hume had become skeptical of religious belief. 2 The term atheism was coined by Sir John Cheke almost two hundred years earlier in 1540, to refer to a lack of belief in divine providence. The term assumed its modern meaning of disbelief in the existence of God, as divine non-existence emerged as a disquieting possibility in the seventeenth century. 14 In early modern Christian Europe, theological knowledge was deemed to derive from two sources. Natural religion attempted to demonstrate God's existence and nature through reason, logic, and observation of the natural world. Revealed religion was based on the premise that the text of the Bible was divinely inspired and thus a source of reliable theological knowledge. 1

Descartes' rationalism had a proof of God's existence at its foundation, but it was also a challenge to the theological methodology established by Thomas Aquinas (1225-1274), which stressed the limitations of human reason, and the need to rely on Biblical revelation. Descartes instead claimed a human capacity to know God and nature through reason alone. However, his rationalist argument for God's existence and guarantorship of the certainty of scientific knowledge was soon rejected as circular. 1415 It was supplanted by Newton's experimental philosophy and Locke's empiricism, both of which stressed experience and observation as sources of the limited knowledge to which humans could aspire, and eschewed metaphysics and speculative hypotheses. 11 Both Newton and Locke were nevertheless devoutly religious, though they held non-standard beliefs. Newton authored an entire volume on Biblical prophesies. 16 Like many natural philosophers associated with the Royal Society, they sought to use the experimental method to demonstrate that the universe exhibited the order and purposefulness of a designed artifact crafted by an all-powerful Intelligence. Hume's Dialogues on Natural Theology (1779) was a response to such hopes, and was to raise devastating objections to them. Unlike Locke, Hume saw that empiricism must place God's existence among those speculative questions to be eschewed. 14 Doubts about God's existence also arose among French intellectuals in the mid-eighteenth century, with the first to openly proclaim himself an atheist being Denis Diderot (1713-1784). 145

Major Contributions

Hume's main philosophical contributions were made via several works. The first was A Treatise of Human Nature published in three volumes in 1739 and 1740, when Hume was 29 years old. Since it sold poorly, Hume recast the material into two later publications, Enquiries concerning Human Understanding, published in 1748, and concerning the Principles of Morals published in 1751. Because of its controversial nature, Hume had Dialogs concerning Natural Religion published posthumously in 1779, three years after his death. 23

Hume and Moral Philosophy

The basic goal of the first three of these works is indicated by the subtitle of the Treatise; "an attempt to introduce the experimental method into moral subjects". 2p.7 Hume sought to extend Newton's experimental philosophy from natural philosophy into what was then called moral philosophy, which he defined as the "science of human nature". 2p.8 The field of moral philosophy was much broader then than today, and included topics that we might classify as psychology or cognitive science, as well as epistemology. To Hume, an understanding of the workings of the mind was the key to establishing the foundations of all other knowledge, including "Mathematics, Natural Philosophy, and Natural Religion". 3p. 34 Natural philosophers, like Newton and Boyle, he maintains, had cured themselves of their "passion for hypotheses and systems". 2p. 8-9 Hume sought to work the same cure for moral philosophy, which he saw as full of speculative metaphysical hypotheses and constant dispute. 2 He proposed an empiricist alternative to a priori metaphysics and its speculative belief systems. He was a naturalist who rejected any appeal to the supernatural in explanations of human nature. For such beliefs, and because he argued that we cannot justify many of our beliefs, he is noted as a skeptic. But he also observed that we have non-rational faculties which compel certain sorts of beliefs (such as the belief that there is a world external to my mind of which my senses provide knowledge), and it is these faculties of which he wishes to give a positive descriptive account. 17

Hume sought to found an empirical science of the mind, based on experience and observation. He noted that the application of the experimental method to "moral subjects" necessarily differed from its use in natural philosophy, because it was impossible to conduct experiments "purposely, with premeditation". Instead, knowledge would be gained "from cautious observation of human life...by men's behaviour in company, in affairs, and in pleasures". 17p. 42 Experimental psychology in the modern sense, with controlled experiments in the laboratory, would not make its appearance until the late 19th century. 18

By the time Hume started work on his Treatise the notion that an idea was the primary sort of mental content dominated European philosophy, due, in part, to the works of Descartes and Locke. Hume instead used the term 'perceptions' to designate mental content of any sort. He supposed there are two sorts of perceptions, impressions and ideas, which was a new distinction. Impressions include feelings we get from our senses, such as of a red tomato currently in front of me, as well as desires, emotions, passions, and sentiments, such as my current hunger for the tomato. Hume distinguished impressions from ideas by their degree of vivacity or force. Thus, I have an impression of the tomato that is currently present, and an idea of a tomato I ate last week. Hume supposed our ideas are faint copies of our impressions. 192017

Noting that there is a regular order to our thoughts, he asserted that the mind has the power to associate ideas. Hume’s concepts about the association of ideas were novel. He posited three associative principles; resemblance (as when I recognize that the tomato currently before me resembles the one in my garden), contiguity in time and place (as when I notice that the tomato is on the table to my left) and causation (as when I notice that bumping the table causes the tomato to tumble to the floor). Hume believed that by thus anatomizing human nature, its laws of operation could be discovered. 217 19 Hume argued that the mind could not be an immaterial substance, though he was also critical of materialism. Regarding personal identity, he wrote that “what we call a mind is nothing but a heap or collection of different perceptions, united together by certain relations, and supos’d, tho’ falsly, to be endow’d with perfect simplicity and identity”. 21p. 182 It was Hume's careful analysis of the mind that led to insights relevant to scientific methodology.

Hume and Scientific Methodology

Hume’s Fork

Aristotle drew a categorical distinction between scientific knowledge or scientia and belief, or opinio. Scientific knowledge was knowledge of causes and proceeded through demonstration, in which a necessary connection between a cause and its effect was proven using premises that were intuitively obvious independently of experience. Corpuscularists retained this demonstrative ideal of scientific explanation. 2 Descartes supposed that a mechanical cause is necessarily related to its effect. A demonstrative science was thus possible, at least in principle, because the general principles of physical nature could be deduced from mathematical principles concerning the shape, size, position, motion, and causal interaction among the ultimate corpuscular particles of matter. The Aristotelian categories of knowledge were thus still accepted by Hume’s contemporaries. However, Newton's method, in which general principles are derived inductively from observation and experiment, did not mesh well with this demonstrative view of science. Newton came to oppose the purely hypothetical explanations of the mechanical philosophy, because they stood in the way of his inductive arguments for universal gravitation. 22

Hume took Newton’s opposition to demonstrative science much further, questioning the idea of a necessary mechanical connection between cause and effect. "Let an object be presented to a man of ever so strong natural reason and abilities;" he wrote, "if that object be entirely new to him, he will not be able, by the most accurate examination of its sensible qualities, to discover any of its causes or effects. Adam [the Biblical first man], though his rational faculties be supposed, at the very first, entirely perfect, could not have inferred from the fluidity and transparency of water, that it would suffocate him, or from the light and warmth of fire, that it would consume him. No object ever discovers, by the qualities which appear to the senses, either the causes, which produced it, or the effects, which will arise from it; nor can our reason, unassisted by experience, ever draw any inference concerning real existence and matter of fact." 13p. 109-110 The connection between a cause and its effect was learned by observation and experience, and could not be shown by demonstrative argument. 23222

Hume recast Aristotle's distinction between knowledge and opinion as a distinction between Relations of ideas and Matters of fact. 13pp. 108-113 Relations of ideas are a priori truths that are discoverable independent of experience, and can be shown with certainty by demonstration or intuition. Because they must be true in any world, they cannot provide any new information about our own world. Relations of ideas are confined to the formal sciences of mathematics, geometry, and logic. Examples of such statements include 'a square’s sides add up to 360 degrees', '1 + 1 = 2', or, 'all bachelors are unmarried'. Relations of ideas can not be denied as their denial would imply a contradiction in their very definition. 213pp. 108-113 Matters of fact, by contrast, are a posteriori statements based on knowledge obtained from the world through observation or experience. Examples of such statements include 'the sky is blue', or 'water is odourless'. Note that the contrary of a matter of fact is not something impossible. The claim that ‘the sun will not rise tomorrow’ is just as intelligible as, and no more contradictory than the claim that ‘the sun will rise tomorrow’. The two claims are only distinguishable by observation and experience. 213pp. 11 Unlike relations of ideas, matters of fact do not hold true in all possible worlds and cannot be established by demonstration. They can never be known with certainty.

Hume’s new categories of knowledge made it clear that natural philosophy, since it relied on knowledge of matters of fact, could never aspire to the kind of certainty that Aristotle supposed for scientific knowledge, and should be content with the modest sort of knowledge available through Newton’s inductive method. 22

Hume’s problem of induction

While championing Newton’s inductive method, Hume also exposed its limitations by showing that conclusions drawn by inductive reasoning could not be rationally justified. As discussed above, Hume argued that knowledge of cause and effect comes only from the constant conjunction of particular phenomena in experience, which allows the use of induction to draw conclusions about cause and effect. 222 Hume envisions such an inductive argument as follows:

1) "I have found that such an object has always been attended with such an effect..."

2) "I foresee, that other objects, which are in appearance, similar, will be attended with similar effects." 13p. 114

Newton supposed that the use of such inductive arguments could be justified by an appeal to the uniformity of nature. 22 Hume however, found a fundamental problem in rationally justifying inductive arguments. Consider the following argument, which might seem to justify our reliance on induction:

1) In the past, the future has been like the past.

2) Therefore, the future will be like the past.

But this argument itself relies on induction, the very mode of argument it seeks to justify. As Hume put it: "According to my account, all arguments about existence are based on the relation of cause and effect; our knowledge of that relation is derived entirely from experience; and in drawing conclusions from experience we assume that the future will be like the past. So if we try to prove this assumption by probable arguments, i.e. arguments regarding existence, we shall obviously be going in a circle, taking for granted the very point that is in question." 24p. 16 He concluded that "the conclusions we draw from experience are not based on reasoning or on any process of understanding". 24p. 15 But induction is necessary for the conclusions that we draw, not only in Newtonian science, but also in our daily lives, which would not be possible without it. Hume concludes that we are compelled to use induction by a powerful natural instinct, or more specifically his principles of association. "All these operations" he wrote, "are species of natural instincts, which no reasoning… is able either to produce or prevent". 13p. 46-47 Humans must, Hume concludes, rely on "the ordinary wisdom of nature", which insures that we form beliefs "by some instinct or mechanical tendency", rather than trusting "the fallacious deductions of our reason". 13p. 55 In keeping with this naturalistic conclusion, Hume devotes an entire section of the Enquiry to an argument that non-human animals also learn by induction. He writes that "it seems evident that animals, like men, learn many things from experience, and infer that the same outcomes will always follow the same causes". 24p. 53 Hume’s conclusion was a radical challenge to the central role assigned by rationalists like Descartes and Leibniz to reason in the production of our knowledge, and is seen today as a step towards modern ideas in cognitive science and neuroscience.

Hume's skepticism about theological knowledge

In the early modern Christian Europe, theology and natural philosophy were not deemed foreign to one another, but rather seen as compatible parts of an integrated mosaic of knowledge. 9p. 65 Theological knowledge derived from observations of nature and its supposed design, the divine revelation of the Bible, and supposed miraculous events where God had intervened directly in human affairs. 1 As a thoroughgoing empiricist, Hume questioned all these sources of knowledge, and rejected theological knowledge as impossible.

In a letter to Henry Home (1696-1782) published in 1737, Hume confessed that he intended to include a skeptical discussion of miracles in his Treatise but left it out for fear of offending readers. Critics of religion in eighteenth century Europe faced the risk of fine, imprisonment, or worse. 1 Hume did later publish his critique in the Enquiry in 1748. He wrote that "A wise man...proportions his belief to the evidence" 24p. 56 and drew the conclusion that "A miracle is a violation of the laws of nature; and because firm and unalterable experience has established these laws, the case against a miracle is- just because it is a miracle- as complete as any argument from experience can possibly be imagined to be....No testimony is sufficient to establish a miracle unless it is of such a kind that its falsehood would be more miraculous than the fact it tries to establish...When anyone tells me that he saw a dead man restored to life, I immediately ask myself whether it is more probable that this person either deceives or has been deceived or that what he reports really has happened...If the falsehood of his testimony would be more miraculous than the event he relates, then he can claim to command my belief or opinion, but not otherwise". 24p. 58-59 The claim that a dead man was restored to life is, of course, central to Christian theology. In 1757, Hume published an essay entitled The Natural History of Religion which was the first systematic attempt to explain religious belief solely in terms of what we would call psychological and sociological factors. 1

Hume's most ambitious skeptical attack on the possibility of theological knowledge was his Dialogues concerning Natural Religion, which he arranged to have published posthumously because of its inflammatory nature. In it, Hume raised devastating objections to the claim that the universe showed evidence of purposeful design by an Intelligent Creator. This claim was then widely popular among natural philosophers associated with the Royal Society 2 The Dialogues is written as a conversation between three characters; Cleanthes, a proponent of the design argument, Demea, a mystic, and Philo, a religious skeptic generally supposed to be Hume's spokesperson. Philo argues that the analogy between the universe and a designed artifact is weak. For example, we experience only one universe and have nothing to compare it to. We recognize human artifacts by contrast with non-artifacts such as rocks. He also notes that we have no experience of the origin of the universe, and that causal inference requires a basis in experienced constant conjunction between two things. For the origin of the universe we have nothing of the sort. Demea deems Cleanthes concept of God as cosmic designer to be anthropomorphic and limiting. In a discussion of the human condition, Philo asks why an infinitely wise, powerful, and good God would permit human suffering. By the end, Hume's characters arguments lead the reader to the conclude, with Philo, that God's nature seems inconceivable, incomprehensible, and indefinable and therefore the question of God's existence is rendered meaningless. 25262

Criticism

, and Hume lamented that the work fell "deadborn from the press". 2p. 4 It is however, today regarded as a major and important work.

Historically, due to the threatening nature of Hume’s distinction between relations of ideas and matters of fact, particularly to Newtonian physics, as well as his problem of induction there have been many critics of Hume. One of the most prominent critics to criticize Hume on the account of his distinction between the types of propositions was Immanuel Kant. Kant criticized Hume, seeking to validate Newton’s propositions about the world which could never be meaningful under Hume’s distinction. Kant theorized that the world was interpreted through sensory and intellect and thus there must exist some sort of a priori synthetic proposition.4 The existence of such a proposition would of course result in a proposition that fit both categories of Hume’s distinction. Unfortunately, Kant’s a priori synthetic proposition was debunked with the arrival of probabilistic determinism.

As for criticisms on Hume's Problem of Induction, there are quite a few cases. One of the more notable cases was the critique Karl Popper had towards Hume, stating that induction is a myth.27 Popper argued science is created by conjecture and criticism rather than reference to the past, and that the main purpose of observations wasn’t to make inferences about the future but to refute present existing theories. Popper was committed to the idea that Hume had incorrectly orientated himself towards a means of justifying knowledge. Popper, instead, preferred to look for a process by which to correct errors.28

Wesley Salmon responded to this criticism in Hume’s place, stating theories still need predictions to be tested. When Popperians have multiple theories, each sharing the same quantity of empirical content, Popperians would choose the theories which were better corroborated but lack any justification in this decision. The Popperians either make an inductive claim:

1. A theory was reliable in the past.
2. It will be reliable in the future having survived falsification.

Or they admit corroboration is not an indication of predictive power.29

Publications

Here are the works of Hume included in the bibliographic records of this encyclopedia:

• Hume (2008): Hume, David. (2008) Enquiry Concerning Human Understanding. Early Modern Texts. Retrieved from http://www.earlymoderntexts.com/authors/hume.
• Hume (2007): Hume, David. (2007) Dialogues Concerning Natural Religion. Early Modern Texts. Retrieved from http://www.earlymoderntexts.com/authors/hume.
• Hume (2000): Hume, David. (2000) A Treatise of Human Nature. Oxford University Press.
• Hume (1975): Hume, David. (1975) Enquiries Concerning Human Understanding and Concerning the Principles of Morals. Oxford University Press.

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