We are reading David Hume in my ethics class now, parts of both An Enquiry Concerning the Principles of Morals and a Treatise of Human Nature. I assign Hume to give students a break from the raving rationalism of Plato, Aristotle, Aquinas, Mill, and Kant. In Book 3, Part 1, Seections 1&2 of the Treatise, Hume says we can only know something is moral or immoral by using what he calls our sentiment (i.e. passion/emotion/feeling).
Take any action allowed to be vicious: Willful murder, for instance. Examine it in all lights, and see if you can find the matter of fact, or real existence, which you call vice. In whichever way you take it, you will find only certain passions, motives, volitions and thoughts. There is no matter of fact in the case. The vice entirely escapes you, as long as you consider the object. You can never find it, till you turn your reflection into your own breast, and find a sentiment of disapprobation, which arises in you, towards this action.
This is interesting enough itself, that we must feel (dis)approbation to make any moral distinctions. But what is also interesting is what he says about reason. He argues that reason cannot be the source of moral distinctions because morality is a realm of action, it is a practical enterprise that helps us know how to act in the world, and reason, he says, cannot produce action. Throughout Book 3 reason is accused of being inactive, indolent, calm, impassive…inert like a noble gas. No wonder Deleuze is so taken with Hume: the latter argues that the human faculty that produces action, that causes us to move, that generates life, is our sentiment, our passion, or, though Hume does not use this word as often, our desire. It is pretty fair to read Hume as arguing that desire is production, and reason is anti-production. Desire creates life, while reason only offers us useful facts about its contours. It recalls the line from Lawrence that D&G are fond of:
‘I wasn’t talking about knowledge…I was talking about the mental life,’ laughed Dukes. ‘Real knowledge comes out of the whole corpus of the consciousness; out of your belly and your penis as much as out of your brain and mind. The mind can only analyse and rationalize. Set the mind and the reason to cock it over the rest, and all they can do is to criticize, and make a deadness. I say all they can do. It is vastly important. Lady Chatterley’s Lover, p. 41.