In this series of posts I wanted to explore one of the key ideas from David Hume’s Treatise of Human Nature. Are our actions motivated by reason or passion? This discussion takes place in two of the three books that form part of the Treatise. In Book 2 Hume puts forth a general principle about the relationship between reason and passion. In Book 3 he applies this principle to the more specific case of making moral decisions. Which of reason and passion should be considered the source of our morality?
The current post considers the following subjects in particular:
- Critiquing the traditional view that reason alone is the source of action
- Defining the two types of knowledge covered by reason
- Why the two types of knowledge can’t be the cause of our actions
Hume starts in Book 2 by critiquing the accepted wisdom of philosophers and non-philosophers alike. Under the traditional view, reason alone determines our actions. Human beings are rational creatures and rationality is considered supreme: ‘every rational creature is obliged to regulate his actions by reason.’ Reason is seen as eternal and divine while the passions are blind, inconstant and deceitful.
In order to reject the view that reason is paramount, Hume sets out the challenge that faces him. He will need to demonstrate that the following two propositions are true: (1) reason alone can never be a motive to any action of the will, and (2) reason can never oppose passion in the direction of the will. As part of this discussion, Hume is only concerned with intentional acts of the will. He accepts that when the will was not free – for instance when it was coerced into action by threats of violence – then the moral agent lacked the necessary freedom to be responsible for the action.
Based on Hume’s earlier discussion in the Treatise, ‘reason’ is most naturally associated with ‘ideas’ (representations of the world based in human thought). Hume has previously defined mental ‘perceptions’ as the combination of both ideas and impressions. As for impressions, these can be subdivided into impressions of sensation and impressions of reflection. The passions form part of impressions of reflection. Since impressions are more lively than ideas, this means that the passions are more lively than rational thoughts.
Hume continues the discussion of ‘reason’ in Book 2. Under his theory of human nature, Hume declares that ‘reason’ consists of two realms of knowledge: demonstrative knowledge (propositions capable of mathematical proof) and probable inferences of cause-and-effect (assumptions based on experiencing ‘constant conjunctions’ between events A and B). Hume’s definition here appears quite restrictive, and doesn’t consider other forms of mental activity such as creativity. For instance, if we wanted to speculate on what life on Mars would be like, it is unclear from Hume what role reason would play. Such ‘free form’ thinking cannot be based on either demonstrative or probable reasoning. In both cases we lack constant conjunctions and therefore also lack evidence of cause-and-effect.
In terms of how the two forms of ‘reason’ impact actions, Hume believes that demonstrative knowledge can never be the cause of any action. This knowledge exists in the world of ideas, which is ‘totally removed’ from the world of volition. All we can obtain from demonstrative knowledge are true and false propositions that direct our own judgements concerning cause and effect. They have no direct and immediate influence over our behaviour. Although Hume rejects demonstrative knowledge as the primary source of action, as part of his argument he indicates that reason still has some role to play. As we’ll see, reason is however ‘one stage removed’ from the true source of our motivation to act.
Frequently throughout the Treatise, Hume will speak of ‘clear proof’ that reason can never be the source of our actions. However, this point is made more as an assertion, without any supporting argument. Is it true that demonstrative knowledge can never be the primary influence of our actions? If my job revolves around mathematical equations (say, working as an engineer at NASA), could you not argue that the results of my calculations have a direct impact on my actions? Hume would however claim in this case that our motivationto act does not come directly from the demonstrative knowledge (the equations), but from another motive, such as an obligation to carry out one’s job in a professional manner.
Hume’s own example of the merchant who desires a total of his accounts is also not so straightforward. If anything, the merchant example appears to support the counter-notion that demonstrative knowledge does help to initiate action. In the example, the merchant wants to know whether he has enough money to repay his debts. He will only know how to act once he has seen the results of the calculations. This appears to be ‘knowledge’ in the pure sense in that it does not require any input from the emotions. The merchant will act one way or the other depending on what sort of result he obtains from the calculations. The ‘passions’ would seem to be of little importance when making decisions of this nature.
How would Hume respond to this? Again, Hume would point out that while the ‘facts’ play an important role in the action about to take place, the merchant is really motivated to act due to some internal feeling, such as a willingness to maintain a good reputation for himself in business. As a result of this motivation, he will do whatever it takes to maintain his reputation, and the result of the account calculation will merely point him in the right direction. Crucially, the willingness to act existed prior to the rational judgement, which for Hume proves that the passions are the primary source of our actions.
With demonstrative knowledge dealt with and discarded, Hume next turns to probable reasoning and considers why this also can’t be the source of our actions. Again, all that our reason is capable of telling us is that knowledge derives from cause-and-effect. As reason is nothing more than the discovery of this relationship, this cannot do anything to impact our actions. We need to have some form of interest in the objects to motivate us to act, and this interest is not something we can ever obtain from reason.
Again, this might not immediately correlate to the everyday sense of how humans make decisions. If I look outside the window and see dark clouds forming in the sky, isn’t my reason making a conclusion about the probable weather, which means I will get wet if I go outside? Aren’t my actions being directly determined by my rational evaluation of the weather? Hume again would argue that I already have an internal motivation to act. I either want to go outside to complete whatever tasks I plan to do, or I don’t want to get wet as I’m afraid I will catch a cold. Similar to the merchant example, the internal decision has already been made but I am still relying on reason to tell me which direction I should go.
Satisfied that neither demonstrative knowledge nor probable reasoning is the motivating force behind our actions, Hume believes he has dealt with the first of his two challenges: reason can never be the sole motivating force behind an action. Hume therefore makes his famous conclusion: reason ought to be considered the slave of the passions. Reason takes on a subservient role, supporting any decision already made by the passions.
Hume will now move onto the second of his challenges. Even if reason isn’t the primary motivating force of our actions, can it still oppose and override a passion?