Hume, David (1711–76)

DOI: 10.4324/9780415249126-DB040-2
Version: v2,  Published online: 2005
Retrieved January 23, 2019, from

9. Scepticism

As the scientific revolution of the seventeenth century brought a decline in the authority of Aristotle, it also brought renewed interest in ancient scepticism (including Pyrrhonism and the scepticism of the later Academy) (see PYRRHONISM; SCEPTICISM, RENAISSANCE), and Descartes’ methodological scepticism in the Meditations helped to make a concern with scepticism central to philosophy. Hume’s strategy in the Treatise is to complete an investigation of human cognitive faculties, by means of those faculties, before turning to the question of whether the nature of the discoveries made undermines confidence in those faculties themselves. Thus, at the conclusion of Book I of the Treatise (THN 1.4.7), Hume surveys a number of considerations conducive to scepticism (to which the additional problem about personal identity from the Appendix to the Treatise constitutes an ex post facto addition). At the conclusion of the first Enquiry, he again surveys and assesses sceptical considerations, although the list only partially overlaps that of the Treatise.

Of the general sceptical considerations concerning human cognition (beyond personal susceptibilities to error) reviewed at the conclusion of the Treatise, the first lies in the dependence of belief on the ‘seemingly trivial’ quality of the imagination whereby ideas acquire force and vivacity from impressions by means of probable reasoning, memory and the senses. (It is only here, incidentally, long after his famous account of probable or inductive reasoning, that he draws any connection between it and scepticism in the Treatise). The second lies in the ‘contradiction’ between causal reasoning and the belief in bodies, with specific qualities, discovered in connection with ‘the modern philosophy’. The third consists in the illusion whereby the mind supposes that it discovers real necessary connections intrinsic to causes and effects themselves, even though such connections are in fact inconceivable.

The final sceptical consideration depends on an argument that Hume had earlier discussed in a section entitled ‘Of scepticism with regard to reason’ (THN 1.4.1). Since reason is a kind of cause, he observes, of which truth is the usual but not unfailing effect, every judgment, with whatever degree of assurance it is held, may be assessed, on the basis of past experience, for the probability that one’s faculties operated well – that is (presumably), did not produce too high a degree of assurance – in reaching that judgment. Yet even if one concludes with a high degree of assurance that one’s faculties operated well in the initial judgment, one will find at least some low degree of probability that one’s original assurance was too high; and this realization should serve to decrease somewhat the original assurance of the first judgment. Furthermore, he argues, a third judgment concerning the operation of one’s faculties in the second judgment will likewise find at least some low degree of probability that one’s assurance in making the second judgment – namely, the judgment that one’s original assurance in the first judgment was not too high – was itself too high. This realization, Hume argues, should properly reduce the assurance of the second judgment – which should, in turn, again reduce further the assurance of the first judgment. Since this process may properly be reiterated indefinitely, and the amount of assurance available in any judgment is finite, the result should, in accordance with the natural operations of the ‘probability of causes’, be the elimination of all belief.

No such elimination of belief actually occurs, however, even when one aims to employ the probability of causes as scrupulously as possible. Hume explains this phenomenon through appeal to another ‘seemingly trivial quality’ of the imagination – the unnatural ascent to higher levels of reflection strains the mind and prevents the successive reflexive reasonings from having their usual effects. When he first considers the question of reason’s reflexive subversion of belief, he dismisses the question of whether he is himself a total sceptic on the grounds that such scepticism cannot be maintained with any constancy, and instead takes the argument as confirmation for his theory that belief consists in vivacity – for this best explains how the trivial quality of the imagination prevents the annihilation of belief.

Nevertheless, the conclusion that causal reasoning would, unless prevented by a seemingly trivial feature of the imagination, naturally annihilate all belief is unquestionably a disturbing one; and Hume returns to it, at the conclusion of his recital of sceptical considerations near the end of Book 1, in order to formulate what he calls a ‘dangerous dilemma’. The dilemma is this: if we reject the trivial quality of the imagination that saves reason from its own reflexive self-subversion, then we must allow that all belief should be rejected; yet if we accept the trivial quality of the imagination by making it a principle to reject all ‘refined and elaborate arguments’, we cut off much of science (which also depends on elaborate arguments); we must, on grounds of parity, accept all other features of the imagination as well, even those that clearly lead to illusion; and we contradict ourselves, for the argument supporting the need to reject refined and elaborate arguments is itself a refined and elaborate argument. The immediate result of this dilemma, Hume reports, is a state of intense and general doubt.

This intense general doubt constitutes a ‘philosophical melancholy and delirium’ that cannot be removed by argument but is naturally unsustainable. It is naturally succeeded, Hume reports, by a mood of ‘indolence and spleen’, in which an irresistible return to belief and reasoning concerning matters of ordinary life is combined with a disposition to avoid philosophizing, which has resulted in such discomfort. He thus finds himself operating in accordance with the principle (sometimes now called the Title Principle): ‘Where reason is lively and mixes itself with some propensity, it ought to be assented to. Where it does not, it can have no title to operate on us’. Yet the state of indolence and spleen itself proves, in turn, to be unstable. For Hume finds naturally arising within him a renewed curiosity concerning philosophical topics and an ambition to contribute to the instruction of mankind and make a name for himself by his discoveries; and his return to philosophy is confirmed by the reflection that philosophy is a safer guide to speculation than is religion. He thus finds that the Title Principle, although originating in indolence and spleen, actually supports philosophical enquiry. Indeed, it avoids the ‘dangerous dilemma’ and provides a principle of belief that he can normatively endorse. For it allows him to discount the ‘unlively’ reasoning of the indefinitely iterated probability of causes that would gradually eradicate belief while nevertheless accepting ‘refined and elaborate arguments’ on topics of interest to him (arguments which thereby ‘mix with some propensity’). His continuing awareness of the ‘infirmities’ of human cognitive nature that he has discovered produce a spirit of moderate scepticism – a ‘diffidence’ in judgment – but he regards those infirmities themselves with diffidence and endorses assent to his faculties (as corrected by reflection), ready to continue the investigations of his science of man into the passions and morals.

At the conclusion of the first Enquiry, Hume distinguishes between antecedent scepticism and consequent scepticism. Antecedent scepticism, which he identifies with the methodological scepticism of Descartes, is scepticism that occurs prior to the investigation of our faculties. It recommends beginning enquiry with universal doubt, even concerning the use of one’s faculties, until those faculties have been validated by reasoning from a principle that cannot possibly be fallacious. Hume rejects this kind of scepticism on the grounds that no one self-evident principle is more certain than others and that no reasoning from such a principle could take place except by means of the very faculties that are supposed to be in doubt. (He does, however, endorse a more moderate antecedent scepticism consisting simply in antecedent caution and impartiality.) Consequent scepticism, in contrast, is scepticism that arises from the results of an investigation of our faculties, and Hume’s own scepticism is of this kind. The results that he cites concern the senses, abstract (that is, demonstrative) reasoning and moral evidence (that is, probable reasoning). The consideration of sensory errors and illusions, he remarks, is a ‘trite’ topic of scepticism, and shows only that the first appearances of the senses often stand in need of correction. A more ‘profound’ sceptical consideration is a feature of the belief in bodies previously explained in the Treatise: namely, that the original version of this belief, identifying impressions themselves as continued and distinct existences, can be shown to be false, while the theory postulating that bodies are the causes of sensory impressions cannot be supported by causal reasoning based on observed constant conjunction. A further ‘profound’ topic, also presented in the Treatise, lies in the ‘contradiction’ between causal reasoning and the belief in bodies that arises from ‘the modern philosophy’. The consideration concerning abstract reasoning lies in mathematical demonstrations of the infinite divisibility of extension, which Hume regards as paradoxical. (He refers in a footnote to the theory of extension he had proposed in the Treatise, according to which finite extensions are composed of finite numbers of unextended minima, as capable of resolving this paradox.) A ‘popular’ objection to moral or probable reasoning lies in the vast diversity of opinions among humankind. A more ‘philosophical’ objection, however, lies in the recognition that we have no argument to convince us that what we have observed to be constantly conjoined in our experience will continue to be so conjoined; only a natural instinct leads us to make this supposition. The Enquiry omits discussion of reasoning’s reflexive annihilation of belief, and hence also of the ‘dangerous dilemma’ that it posed. Nor is there any mention of the Title Principle, of the stage of ‘indolence and spleen’ that gave rise to it, or the role of curiosity and ambition in motivating a return to philosophy. There is, however, a distinction between ‘Pyrrhonian’ or ‘excessive’ scepticism, on the one hand, and ‘Academic’ or ‘mitigated’ scepticism on the other. Intense contemplation of sceptical considerations naturally produces a ‘tincture’ of Pyrrhonian scepticism that is useful in moderating dogmatic self-confidence. Were Pyrrhonian doubt to remain constant, however, it would destroy human life by preventing action. Fortunately, however, the sources of belief in human nature are too powerful to allow this to occur, and the natural outcome of reflection on sceptical considerations is a more durable Academic scepticism that consists in a certain diffidence, modesty and lack of dogmatism in all one’s judgments plus a determination to refrain from all ‘high and distant enquiries’ beyond our faculties – such as cosmological speculation concerning ‘the origins of worlds’ – that have no connection to ‘common life’. Hume in the Enquiry recommends and endorses this mitigated scepticism, which he judges to be socially useful, he with a rousing call for the elimination of scholastic metaphysics and theology not based on mathematical or experimental reasoning: ‘Commit it then to the flames: for it can contain nothing but sophistry and illusion’.

In order to characterize Hume’s scepticism, it is useful to distinguish several different dimensions in which scepticism can vary. One of these is its scope – that is, the range of propositions to which it applies. Another is its character – that is, whether it consists in actual doubt, in a normative injunction to doubt, in a theoretical claim that a proposition lacks support through reasoning, or in a claim that a proposition lacks epistemic merit. A third is its degree – that is, whether it is unmitigated or mitigated. A fourth is its basis – that is, whether it is antecedent to enquiry or consequent to it. A fifth is its constancy – that is, whether it is constant or variable. In these terms, all of Hume’s scepticism appears to be consequent to enquiry. He both engages in and recommends a mitigated doubt concerning all topics, as well as unmitigated doubt concerning ‘high and distant’ enquiries. The actual doubt in which he engages with respect to other topics is somewhat variable – potentially unmitigated in rare moments when intensely considering sceptical topics, and sometimes entirely absent in moments of special conviction. He unmitigatedly rejects the claim that the uniformity of nature and the belief in bodies originate with support through reasoning. But he is not committed to the view that only propositions produced or supported by reasoning have epistemic merit. On the contrary, as his endorsement of the Title Principle and his preference for ‘wise’ beliefs over unphilosophical probability indicate, his mitigated scepticism about the epistemic merit of beliefs generally allows him to hold that many beliefs have some degree of epistemic merit.

Citing this article:
Garrett, Don. Scepticism. Hume, David (1711–76), 2005, doi:10.4324/9780415249126-DB040-2. Routledge Encyclopedia of Philosophy, Taylor and Francis,
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