Hume’s scepticism about practical reason

ac64ea67cb611ae3e62e566249a32c3bI shall endeavour to explain and assess Hume’s scepticism about practical reason by dividing this essay into three parts: in the first part, I will expound Hume’s view on reason and passion, based on which he argues that moral distinctions are not derived from reason, for it is merely the discernment of ‘truth and falsehood’ and is ‘utterly impotent in this particular’[1]. I shall argue, in the second part, that his account of passion and action is tautological, for his broad definition of ‘passion’ will allow him to attribute any actions, be it in accordance, or, in direct conflict, with immediate bodily inclinations, to ‘passion’, and thus renders his account of practical reason vulnerable to attacks.  


For Hume’s argument over reason is interwoven with the discussion of action and morality, I shall expound it alongside his doctrine of morals. Hume’s explication of reason is twofold: ‘first’, he writes in the beginning of Book II Section III of the Treatise, that ‘reason alone can never be a motive to any action of the will; and secondly, that it can never oppose passion in the direction of the will.’ The first part of his argument can be expressed negatively, with reference to morals, as reason being ‘incapable of determining the distinction between good and evil’[2], whilst the latter part can be stated positively as moral judgments are determined by ‘the sentiments of approval and disapproval which Nature has caused to arise in us upon the contemplation of this or that action or situation’[3]. I shall hereafter call them the negative and positive statements respectively.

Before proceeding to explicate Hume’s scepticism about practical reason, a brief explanation on Hume’s theory of human understanding is in order, for his explication of human’s understanding constitutes the core of the first part of his argument over reason, i.e., ‘reason alone can never be a motive to any action of the will’. He categorises human perception into two types, viz., impressions and ideas:—

‘Here therefore we may divide all the perceptions of the mind into two classes or species, which are distinguished by their different degrees of force and vivacity. The less forcible and lively are commonly denominated Thoughts or Idea. The other species…Impressions…By the term impression…I mean all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will.’[4]

Whence he develops his theory of human understanding as follows, summarised by Stroud[5]:—

  • ‘There is no thought or mental activity unless there is a perception before the mind.’
  • ‘Every perception is either an impression or an idea.’
  • ‘Every perception is either simple or complex.’
  • ‘Every complex perception consists completely of simple perceptions.’
  • ‘For every simple idea there is a corresponding simple impression.’
  • ‘Every simple idea arises in the mind as the effect of its corresponding simple impression.’
  • ‘There are no impressions of reflection without some impression of sensation.’


  • ‘There is no thought or mental activity unless there are impressions of sensation.’

[Direct quote from Stroud in Italic]

Hume’s view, which follows from the above logical induction that no thought or mental activity is possible unless there are impressions of sensation, confines him to believe that sensory experience (perception) is the only ground for making judgments—he ascribes the decision-making process of an individual to only his perception.

This hard empiricist position that Hume takes gives credence to his analysis of the role reason plays in making moral judgments—he recognises, based on his theory of human understanding, that moral distinctions cannot be discerned by reason. For being ‘reasonable or unreasonable’, to him, is merely a distinction being made in accordance with the semblance that ‘copies of things’ bear to empirical facts.

It follows that moral belief, having no reference to anything else, cannot be discerned as ‘reasonable or unreasonable’ and ‘not susceptible to any such agreement or disagreement’[6], for it is an impression (fact), not an idea (copy). This gives rise to his recognition of the ‘inactive character of reason’. Reasoning, for Hume, is ontologically the discernment of truth—‘the arbiter in all questions of truth and of fact’[7]. It can merely demonstrate the abstract connections of ideas, and ‘relations of matters of facts’, as ‘to know propositions is just to know propositions. It is not to prefer, to act, or even to refrain’[8]. After recognising reason is but a faculty of discerning ‘what is’, we can perhaps see a clearer picture of what Hume’s scepticism about practical reason truly is: it stems from his drawing up of a logical distinction between facts and values, whence he derives—what is now commonly known, eponymously, as the ‘Hume’s Law’[9]—that ‘ought’ cannot be derived from ‘is’:—

‘In every system of morality…I have always remarked, that the author proceeds for some time in the ordinary ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not…For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it should be observed and explained; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.’[10]

Hume states that reason, being a faculty that is concerned with ‘truth or falsehood’, cannot logically give rise to a motive, which is expressed in an ‘ought/ought not’ proposition. Reason can therefore be seen as ‘incapable of determining the distinction between good and evil’ in two senses, i.e., (i) ‘good and evil’ is not an idea, but an impression, which cannot be discerned as ‘reasonable or unreasonable’, because it is a ‘real existence’ and is ‘compleat in [it]sel[f]’[11]; (ii) reason cannot provide an ‘ought/ought not’ proposition, for it is merely a faculty of discerning the facts (‘truth and falsehood’). Reason hence cannot be a source of motivation but merely works to either identify and discern the means to one’s ends, in the service of one’s passion:—

‘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.’[12]

Reason is the ‘slave of the passions’ in the sense that it does not initiate, but merely assists the attainment of desire in two ways, (i) it informs an individual the existence of a desired object (e.g. through organising one’s sensory impressions, for instance, redness, roundness, and the scent of sweetness, into a meaningful piece of information: ‘the existence of an apple’); and, (ii) it discerns the means to attaining the object (e.g. through begging, or paying money to the grocer, or stealing)[13]. This brings us to the second part of our explication of Hume’s argument over reason, i.e., that ‘[r]eason can never oppose passion in the direction of the will’.

Hume’s claim that ‘reason can never oppose passion in the direction of the will’ and that it ‘cannot move us to action’ follow from his explication that actions and passions, which are impression, cannot be discerned as ‘reasonable or unreasonable’[14], for they are ‘real existence’ and ‘compleat in themselves’[15]. For Hume, the notion ‘reasonable or unreasonable’ applies only to ideas, which are copies of, and hence bear different levels of semblance to, impressions (empirical facts). The faculty of reason, meanwhile, is merely the discernment of true or false copies. Reason, passion, and action, according to Hume, form a triadic relationship in the process of decision-making: action is initiated by the conjuncture of passion and reason, in which, if exemplified with the operation of a car, passion will serve as the throttle and reason the steering wheel: a non-steered car can move arbitrarily given that the gas pedal is stepped upon, as if it were in the case of a mad man, who acts without the guidance of reason; a man, however, will not be able to perform any actions without the drive of passion, for a car without a throttle will hardly move, despite being steered.

So far I have explicated Hume’s scepticism about practical reason, I shall now move on to access it. Hume, who induced that mental activity is possible unless there are impressions of sensation, confines himself to the belief that judgments stem only from perceptions, as Hegel remarks: ‘whatever true [for the empiricists] must be in the actual world and present to sensation’[16]. Based on such a view, Hume denies the capacity of practical reason in the making of moral judgments and inexorably leads him to equate moral judgement with passion[17].

This will inevitably create an enigma that whomever takes the position of Hume will be hard to justify himself that it is possible for an individual to distance himself from any of his desire and inclination and acts in a way that he regards as morally obligatory, but is in direct conflict with his bodily inclinations nevertheless—an objection that Kant, who thinks that the only possible way to address to the question would be to attribute actions to transcendental reason, would take to that remark, with reference to the ‘categorical imperative’. Hume does endeavour to address to the conflicts between hedonic desires and anhedonic deeds by introducing the distinction of two kinds of desire, viz., that which emanates from ‘certain instincts originally implanted in out natures, such as benevolence and resentment, the love of life, and kindness to children’[18]; and that which he called ‘the general appetite to good and aversion to evil, considered merely as such’[19]—the latter he refers to as ‘calm passion’:—

‘Besides good and evil, or, in other words, pleasure and pain, the direct passions frequently arise from a natural impulse or instinct, which is perfectly unaccountable. Of this kind is the desire of punishment to our enemies, and of happiness to our friends; hunger, thirst, and a few other bodily appetites. These passions, properly speaking, produce good and evil and proceed not from them, like the other affections.’[20]

However, the fact that Hume considers that behind any deed of an individual there is some sort of passion at work seems tautological—he attributes actions to passion and defines the notion of ‘passion’ not confining only to ‘hedonic passion’, but includes what he called ‘calm passion’ as well—the operations of which are often called ‘reason’[21]. This will allow Hume to ascribe any actions to ‘passion’ given its broad definition. Whilst he is justified in identifying reason as merely a faculty for the discernment of facts, and, by the introduction of the ‘Hume’s Law’, he made a strong case for his scepticism about practical reason, Hume has not succeeded in showing ‘passion’ being the only source for motivating actions, for his notion of ‘passion’ is too broadly defined to rule out the logical possibility of attributing actions to intuitive reason[22], which is ontologically different (for it tells us what we ought to do) yet bears striking semblance to ‘calm passion’, in the sense that, though, it is not ‘passion’ as such, it nevertheless can guide one’s conduct insofar as it appeals to his desire to do what is right[23]. As Mackie remarks: ‘we have no overwhelmingly or immediately cogent reason for adopting [Hume’s] theory and rejecting the other, but will have to decide in the end which gives the best overall explanation of the whole range of relevant data and experiences.’[24]

[1] David Hume, A Treatise of Human Nature (Oxford: Clarendon Press, 1978), 457.

[2] Norman Kemp Smith, The Philosophy of David Hume (London: Macmillan, 1941), 193.

[3] Loc. cit.

[4] David Hume, An Enquiry concerning Human Understanding (Oxford: Clarendon Press, 2000), 13-14.

[5] Barry Stroud, Hume (London: Routledge & Kegan Paul, 1977), 22.

[6] Hume, Treatise, 459.

[7] Kemp Smith, Op. cit., 199.

[8] Antony Flew, David Hume (Oxford: Basil Blackwell, 1986), 145.

[9] Loc. cit.

[10] Hume, Treatise, 469.

[11] Jonathan Harrison, Hume’s Moral Epistemology (Oxford: Clarendon Press, 1976), 17.

[12] Hume, Treatise, 415.

[13] Harrison, Op. cit., 5.

[14] Hume, Treatise, 458.

[15] Harrison, Op. cit., 17.

[16] Georg W. F. Hegel, Logic, trans. William Wallace (Oxford: Clarendon Press, 1978), 61 (§38).

[17] Hume, Treatise, 414.

[18] Hume, Treatise, 417.

[19] Loc. cit.

[20] Hume, Treatise, 439.

[21] J. L. Mackie, Hume’s Moral Theory (Routledge & Kegan Paul, 1980), 47.

[22] William C. Swabey, Ethical Theory from Hobbes to Kant (New York: The Citadel Press, 1961), 147.

[23] Loc. cit.

[24] Mackie, Op. cit., 49.



Barry Stroud, Hume. London: Routledge & Kegan Paul, 1977.

Flew, Antony. David Hume. Oxford: Basil Blackwell, 1986.

Harrison, Jonathan. Hume’s Moral Epistemology. Oxford: Clarendon Press, 1976.

Hegel, Georg W. F. Logic. Translated by William Wallace. Oxford: Clarendon Press, 1978.

Hume, David. An Enquiry concerning Human Understanding. Edited by Tom L. Beauchamp. Oxford: Clarendon Press, 2000.

Hume, David. A Treatise of Human Nature. Edited by L. A. Selby-Bigge. Oxford: Clarendon Press, 1978.

Kemp Smith, Norman. The Philosophy of David Hume. London: Macmillan, 1941.

Mackie, J. L. Hume’s Moral Theory. Routledge & Kegan Paul, 1980.

Swabey, William C. Ethical Theory from Hobbes to Kant. New York: The Citadel Press, 1961.

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