Hume, along with Thomas Hobbes, is cited as a classical compatibilist about the notions of freedom and determinism. Compatibilism seeks to reconcile human freedom with the mechanist view that human beings are part of a deterministic universe, which is completely governed by physical laws. Hume, on this point, was influenced greatly by the scientific revolution, particularly by Sir Isaac Newton. Hume argued that the dispute between freedom and determinism continued over 2000 years due to ambiguous terminology. He wrote: "From this circumstance alone, that a controversy has been long kept on foot…we may presume that there is some ambiguity in the expression," and that different disputants use different meanings for the same terms.
Hume defines the concept of necessity as "the uniformity, observable in the operations of nature; where similar objects are constantly conjoined together," and liberty as "a power of acting or not acting, according to the determinations of the will." He then argues that, according to these definitions, not only are the two compatible, but liberty requires necessity. For if our actions were not necessitated in the above sense, they would "have so little in connexion with motives, inclinations and circumstances, that one does not follow with a certain degree of uniformity from the other." But if our actions are not thus connected to the will, then our actions can never be free: they would be matters of "chance; which is universally allowed to have no existence." Australian philosopher John Passmore writes that confusion has arisen because "necessity" has been taken to mean "necessary connexion." Once this has been abandoned, Hume argues that "liberty and necessity will be found not to be in conflict one with another."
Moreover, Hume goes on to argue that in order to be held morally responsible, it is required that our behaviour be caused or necessitated, for, as he wrote:
Actions are, by their very nature, temporary and perishing; and where they proceed not from some cause in the character and disposition of the person who performed them, they can neither redound to his honour, if good; nor infamy, if evil.
Hume describes the link between causality and our capacity to rationally make a decision from this an inference of the mind. Human beings assess a situation based upon certain predetermined events and from that form a choice. Hume believes that this choice is made spontaneously. Hume calls this form of decision making the liberty of spontaneity.
Education writer Richard Wright considers that Hume's position rejects a famous moral puzzle attributed to French philosopher Jean Buridan. The Buridan's ass puzzle describes a donkey that is hungry. This donkey has separate bales of hay on both sides, which are of equal distances from him. The problem concerns which bale the donkey chooses. Buridan was said to believe that the donkey would die, because he has no autonomy. The donkey is incapable of forming a rational decision as there is no motive to choose one bale of hay over the other. However, human beings are different, because a human who is placed in a position where he is forced to choose one loaf of bread over another will make a decision to take one in lieu of the other. For Buridan, humans have the capacity of autonomy, and he recognises the choice that is ultimately made will be based on chance, as both loaves of bread are exactly the same. However, Wright says that Hume completely rejects this notion, arguing that a human will spontaneously act in such a situation because he is faced with impending death if he fails to do so. Such a decision is not made on the basis of chance, but rather on necessity and spontaneity, given the prior predetermined events leading up to the predicament.
Hume's argument is supported by modern-day compatibilists such as R. E. Hobart, a pseudonym of philosopher Dickinson S. Miller. However, P. F. Strawson argued that the issue of whether we hold one another morally responsible does not ultimately depend on the truth or falsity of a metaphysical thesis such as determinism. This is because our so holding one another is a non-rational human sentiment that is not predicated on such theses.
The cornerstone of Hume's epistemology is the problem of induction. This may be the area of Hume's thought where his scepticism about human powers of reason is most pronounced. The problem revolves around the plausibility of inductive reasoning, that is, reasoning from the observed behaviour of objects to their behaviour when unobserved. As Hume wrote, induction concerns how things behave when they go "beyond the present testimony of the senses, or the records of our memory". Hume argues that we tend to believe that things behave in a regular manner, meaning that patterns in the behaviour of objects seem to persist into the future, and throughout the unobserved present. Hume's argument is that we cannot rationally justify the claim that nature will continue to be uniform, as justification comes in only two varieties—demonstrative reasoning and probable reasoning[iii]—and both of these are inadequate. With regard to demonstrative reasoning, Hume argues that the uniformity principle cannot be demonstrated, as it is "consistent and conceivable" that nature might stop being regular. Turning to probable reasoning, Hume argues that we cannot hold that nature will continue to be uniform because it has been in the past. As this is using the very sort of reasoning (induction) that is under question, it would be circular reasoning. Thus, no form of justification will rationally warrant our inductive inferences.
Hume's solution to this problem is to argue that, rather than reason, natural instinct explains the human practice of making inductive inferences. He asserts that "Nature, by an absolute and uncontroulable [sic] necessity has determin'd us to judge as well as to breathe and feel." In 1985, and in agreement with Hume, John D. Kenyon writes:
Reason might manage to raise a doubt about the truth of a conclusion of natural inductive inference just for a moment ... but the sheer agreeableness of animal faith will protect us from excessive caution and sterile suspension of belief.
Others, such as Charles Sanders Peirce, have demurred from Hume's solution, while some, such as Kant and Karl Popper, have thought that Hume's analysis has "posed a most fundamental challenge to all human knowledge claims".
The notion of causation is closely linked to the problem of induction. According to Hume, we reason inductively by associating constantly conjoined events. It is the mental act of association that is the basis of our concept of causation. At least three interpretations of Hume's theory of causation are represented in the literature:
the logical positivist; the sceptical realist; and the quasi-realist.
Hume acknowledged that there are events constantly unfolding, and humanity cannot guarantee that these events are caused by prior events or are independent instances. He opposed the widely accepted theory of causation that 'all events have a specific course or reason'. Therefore, Hume crafted his own theory of causation, formed through his empiricist and sceptic beliefs. He split causation into two realms: "All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact." Relations of Ideas are a priori and represent universal bonds between ideas that mark the cornerstones of human thought. Matters of Fact are dependent on the observer and experience. They are often not universally held to be true among multiple persons. Hume was an Empiricist, meaning he believed "causes and effects are discoverable not by reason, but by experience". He goes on to say that, even with the perspective of the past, humanity cannot dictate future events because thoughts of the past are limited, compared to the possibilities for the future. Hume's separation between Matters of Fact and Relations of Ideas is often referred to as "Hume's fork."
Hume explains his theory of causation and causal inference by division into three different parts. In these three branches he explains his ideas and compares and contrasts his views to his predecessors. These branches are the Critical Phase, the Constructive Phase, and Belief. In the Critical Phase, Hume denies his predecessors' theories of causation. Next, he uses the Constructive Phase to resolve any doubts the reader may have had while observing the Critical Phase. "Habit or Custom" mends the gaps in reasoning that occur without the human mind even realising it. Associating ideas has become second nature to the human mind. It "makes us expect for the future, a similar train of events with those which have appeared in the past". However, Hume says that this association cannot be trusted because the span of the human mind to comprehend the past is not necessarily applicable to the wide and distant future. This leads him to the third branch of causal inference, Belief. Belief is what drives the human mind to hold that expectancy of the future is based on past experience. Throughout his explanation of causal inference, Hume is arguing that the future is not certain to be repetition of the past and that the only way to justify induction is through uniformity.
The logical positivist interpretation is that Hume analyses causal propositions, such as "A causes B", in terms of regularities in perception: "A causes B" is equivalent to "Whenever A-type events happen, B-type ones follow", where "whenever" refers to all possible perceptions. In his Treatise of Human Nature, Hume wrote:
Power and necessity…are…qualities of perceptions, not of objects…felt by the soul and not perceiv'd externally in bodies.
This view is rejected by sceptical realists, who argue that Hume thought that causation amounts to more than just the regular succession of events.[ii] Hume said that, when two events are causally conjoined, a necessary connection underpins the conjunction:
Shall we rest contented with these two relations of contiguity and succession, as affording a complete idea of causation? By no means…there is a necessary connexion to be taken into consideration.
Angela Coventry writes that, for Hume, "there is nothing in any particular instance of cause and effect involving external objects which suggests the idea of power or necessary connection" and "we are ignorant of the powers that operate between objects". However, while denying the possibility of knowing the powers between objects, Hume accepted the causal principle, writing: "I never asserted so absurd a proposition as that something could arise without a cause."
It has been argued that, while Hume did not think that causation is reducible to pure regularity, he was not a fully-fledged realist either. Simon Blackburn calls this a quasi-realist reading, saying that "Someone talking of cause is voicing a distinct mental set: he is by no means in the same state as someone merely describing regular sequences." In Hume's words, "nothing is more usual than to apply to external bodies every internal sensation, which they occasion".
Empiricist philosophers, such as Hume and Berkeley, favoured the bundle theory of personal identity. In this theory, "the mind itself, far from being an independent power, is simply 'a bundle of perceptions' without unity or cohesive quality". The self is nothing but a bundle of experiences linked by the relations of causation and resemblance; or, more accurately, the empirically warranted idea of the self is just the idea of such a bundle. According to Hume:
For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception. When my perceptions are removed for any time, as by sound sleep; so long I am insensible of myself, and may truly be said not to exist.
— A Treatise of Human Nature, Book I.iv, section 6
This view is supported by, for example, positivist interpreters, who have seen Hume as suggesting that terms such as "self", "person", or "mind" refer to collections of "sense-contents". A modern-day version of the bundle theory of the mind has been advanced by Derek Parfit in his Reasons and Persons.
However, some philosophers have criticised Hume's bundle-theory interpretation of personal identity. They argue that distinct selves can have perceptions that stand in relation to similarity and causality. Thus, perceptions must already come parcelled into distinct "bundles" before they can be associated according to the relations of similarity and causality. In other words, the mind must already possess a unity that cannot be generated, or constituted, by these relations alone. Since the bundle-theory interpretation portrays Hume as answering an ontological question, philosophers like Galen Strawson see Hume as not very concerned with such questions and have queried whether this view is really Hume's. Instead, Strawson suggests that Hume might have been answering an epistemological question about the causal origin of our concept of the self. In the Appendix to the Treatise, Hume declares himself dissatisfied with his earlier account of personal identity in Book 1. Corliss Swain notes that "Commentators agree that if Hume did find some new problem" when he reviewed the section on personal identity, "he wasn't forthcoming about its nature in the Appendix." One interpretation of Hume's view of the self, argued for by philosopher and psychologist James Giles, is that Hume is not arguing for a bundle theory, which is a form of reductionism, but rather for an eliminative view of the self. Rather than reducing the self to a bundle of perceptions, Hume rejects the idea of the self altogether. On this interpretation, Hume is proposing a "no-self theory" and thus has much in common with Buddhist thought (see anattā). Psychologist Alison Gopnik has argued that Hume was in a position to learn about Buddhist thought during his time in France in the 1730s.
Practical reason relates to whether standards or principles exist that are also authoritative for all rational beings, dictating people's intentions and actions. Hume is mainly considered an anti-rationalist, denying the possibility for practical reason, although other philosophers such as Christine Korsgaard, Jean Hampton, and Elijah Millgram claim that Hume is not so much of an anti-rationalist as he is just a sceptic of practical reason.
Hume denied the existence of practical reason as a principle because he claimed reason does not have any effect on morality, since morality is capable of producing effects in people that reason alone cannot create. As Hume explains in A Treatise of Human Nature (1740):: 457
Morals excite passions, and produce or prevent actions. Reason of itself is utterly impotent in this particular. The rules of morality, therefore, are not conclusions of our reason."
Since practical reason is supposed to regulate our actions (in theory), Hume denied practical reason on the grounds that reason cannot directly oppose passions. As Hume puts it, "Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them." Reason is less significant than any passion because reason has no original influence, while "A passion is an original existence, or, if you will, modification of existence.": 415
Practical reason is also concerned with the value of actions rather than the truth of propositions, so Hume believed that reason's shortcoming of affecting morality proved that practical reason could not be authoritative for all rational beings, since morality was essential for dictating people's intentions and actions.
Philosopher Paul Russell (2005) contends that Hume wrote "on almost every central question in the philosophy of religion", and that these writings "are among the most important and influential contributions on this topic." Touching on the philosophy, psychology, history, and anthropology of religious thought, Hume's 1757 dissertation "The Natural History of Religion" argues that the monotheistic religions of Judaism, Christianity, and Islam all derive from earlier polytheistic religions. He went on to suggest that all religious belief "traces, in the end, to dread of the unknown". Hume had also written on religious subjects in the first Enquiry, as well as later in the Dialogues Concerning Natural Religion.
Although he wrote a great deal about religion, Hume's personal views have been the subject of much debate.[iv] Some modern critics have described Hume's religious views as agnostic or have described him as a "Pyrrhonian skeptic". Contemporaries considered him to be an atheist, or at least un-Christian, enough so that the Church of Scotland seriously considered bringing charges of infidelity against him. Evidence of his un-Christian beliefs can especially be found in his writings on miracles, in which he attempts to separate historical method from the narrative accounts of miracles. Nevertheless, modern scholars have tended to dismiss the claims of Hume's contemporaries describing him as an atheist as coming from religiously intolerant people who did not understand Hume’s philosophy. The fact that contemporaries suspected him of atheism is exemplified by a story Hume liked to tell:
The best theologian he ever met, he used to say, was the old Edinburgh fishwife who, having recognized him as Hume the atheist, refused to pull him out of the bog into which he had fallen until he declared he was a Christian and repeated the Lord's prayer.
However, in works such as "Of Superstition and Enthusiasm", Hume specifically seems to support the standard religious views of his time and place. This still meant that he could be very critical of the Catholic Church, dismissing it with the standard Protestant accusations of superstition and idolatry,: 70 as well as dismissing as idolatry what his compatriots saw as uncivilised beliefs. He also considered extreme Protestant sects, the members of which he called "enthusiasts", to be corrupters of religion. By contrast, in "The Natural History of Religion", Hume presents arguments suggesting that polytheism had much to commend it over monotheism. Additionally, when mentioning religion as a factor in his History of England, Hume uses it to show the deleterious effect it has on human progress. In his Treatise of Human Nature, Hume wrote: "Generally speaking, the errors in religions are dangerous; those in philosophy only ridiculous."
Lou Reich (1998) argues that Hume was a religious naturalist and rejects interpretations of Hume as an atheist. Paul Russell (2008) writes that Hume was plainly sceptical about religious belief, although perhaps not to the extent of complete atheism. He suggests that Hume's position is best characterised by the term "irreligion," while philosopher David O'Connor (2013) argues that Hume's final position was "weakly deistic". For O'Connor, Hume's "position is deeply ironic. This is because, while inclining towards a weak form of deism, he seriously doubts that we can ever find a sufficiently favourable balance of evidence to justify accepting any religious position." He adds that Hume "did not believe in the God of standard theism ... but he did not rule out all concepts of deity", and that "ambiguity suited his purposes, and this creates difficulty in definitively pinning down his final position on religion".
One of the traditional topics of natural theology is that of the existence of God, and one of the a posteriori arguments for this is the argument from design or the teleological argument. The argument is that the existence of God can be proved by the design that is obvious in the complexity of the world, which Encyclopædia Britannica states is "the most popular", because it is:[unreliable source?]
...the most accessible of the theistic arguments ... which identifies evidences of design in nature, inferring from them a divine designer ... The fact that the universe as a whole is a coherent and efficiently functioning system likewise, in this view, indicates a divine intelligence behind it.
In An Enquiry Concerning Human Understanding, Hume wrote that the design argument seems to depend upon our experience, and its proponents "always suppose the universe, an effect quite singular and unparalleled, to be the proof of a Deity, a cause no less singular and unparalleled". Philosopher Louise E. Loeb (2010) notes that Hume is saying that only experience and observation can be our guide to making inferences about the conjunction between events. However, according to Hume:
We observe neither God nor other universes, and hence no conjunction involving them. There is no observed conjunction to ground an inference either to extended objects or to God, as unobserved causes.
Hume also criticised the argument in his Dialogues Concerning Natural Religion (1779). Hume proposes a finite universe with a finite number of particles. Given infinite time, these particles could randomly fall into any arrangement, including our seemingly designed world.
A century later, the idea of order without design was rendered more plausible by Charles Darwin's discovery that the adaptations of the forms of life result from the natural selection of inherited characteristics.[unreliable source?] For philosopher James D. Madden, it is "Hume, rivaled only by Darwin, [who] has done the most to undermine in principle our confidence in arguments from design among all figures in the Western intellectual tradition".
Finally, Hume discussed a version of the anthropic principle, which is the idea that theories of the universe are constrained by the need to allow for man's existence in it as an observer. Hume has his sceptical mouthpiece Philo suggest that there may have been many worlds, produced by an incompetent designer, whom he called a "stupid mechanic". In his Dialogues Concerning Natural Religion, Hume wrote:
Many worlds might have been botched and bungled throughout an eternity, ere this system was struck out: much labour lost: many fruitless trials made: and a slow, but continued improvement carried on during infinite ages in the art of world-making.
American philosopher Daniel Dennett has suggested that this mechanical explanation of teleology, although "obviously ... an amusing philosophical fantasy", anticipated the notion of natural selection, the 'continued improvement' being like "any Darwinian selection algorithm".