David Hume and the sensible knave

Michelle asked:

Discuss Hume’s response to Glaucon’s challenge

Answer by Craig Skinner

In brief:

Glaucon’s challenge is ‘Why should I be moral, if I can be immoral when it suits me, and can get away with it without loss of reputation?’

Hume has no better answer than Socrates does.

To enlarge:

In book two of Plato’s Republic, telling the story of Gyges who finds an invisibility ring and, using its powers, kills the king, marries the queen and takes all the riches of the kingdom, Glaucon asks Socrates which of us would act differently if we had this kind of power. He challenges Socrates to prove that it is always better to be moral (‘just’), rather than to be immoral even if the latter goes undetected and brings great benefit. Socrates spends the rest of the Republic trying to do this. He claims that immorality always brings psychological damage, and even claims that a moral person who is reviled, rejected, and unjustly regarded as immoral is still happier than an undetected immoral person who is rich and well-respected. Readers of Republic find Glaucon’s question more compelling than Socrates’ answer, and moral philosophers have struggled ever since to better it and to come up with a good argument that will convince an egoist to be moral.

Hume’s response notes the problem, endorses Socrates’ view that immorality damages a person’s integrity and peace of mind, makes the point that in practice immorality risks loss of reputation and future trust, but confesses to no good answer to the determined, careful egoist.

Thus, he says (An Enquiry Concerning the Principals of Morals, Sect. 9, 22-25).

‘…a sensible knave….may think that an act of iniquity….will make a considerable addition to his fortune, without causing any considerable breach in the social union…. That honesty is the best policy, may be a good general rule, but is liable to many exceptions: and he, it may perhaps be thought, conducts himself with most wisdom, who observes the general rule, and takes advantage of all the exceptions. I must confess that, if a man think that this reasoning much requires an answer, it would be a little difficult to find any which will to him appear satisfactory and convincing.’


‘Inward peace of mind, consciousness of integrity… these are very requisite to happiness… knaves… have sacrificed the invaluable enjoyment of a character for the acquisition of worthless toys…’.

We are not asking why people in general should be moral. As Hobbes said, life in a society with no morality would be solitary, poor, nasty brutish and short. No, the immoral person wants to live in a generally moral society but to take advantage of it in her own self-interest. We are asking why an individual should herself be moral.

Suggested justifications are:

1. God commands it.
2. Makes for fulfilling life.
3. Irrational to do otherwise.

1. God commands it.

Even assuming there are any gods, obeying them for fear of punishment or hope of reward smacks of self-interest. No, just as a (good) god would command the rules because they are good, so we should follow them for this reason. But the egoist disagrees and we are no further on.

2. Makes for fulfilling life.

This is Socrates’ view, later Aristotle’s, Hume’s and modern virtue ethicists’. Virtue is necessary for eudaimonia (flourishing) according to our nature as rational, social, child-rearing mammals. I have sympathy with this view, that the ruthless, wealthy mobster is ignorant of what

constitutes real happiness. But I accept that the sensible knave can simply say it’s crazy to deny Gyges had a good life: he married a queen and ruled a kingdom, what more do you want?

3. Acting immorally is irrational.

This is one strand in the eudaimonic argument (2. above). But is famously the Kantian view, that the moral law is what we legislate for ourselves as rational autonomous beings, so that, being rational agents, we follow it, and to do otherwise is irrational. But again, the egoist can simply

say that she formulates maxims for her own interests and rationally follows them.

For completeness, more recent attempts by Nagel, Parfit and Alison Hills to cast doubt on the rationality or coherence of the egoist position, are, in my view, unconvincing.

In conclusion there is no knockdown argument that can convince a determined egoistic, immoral, ‘sensible knave’ to be moral, no Holy Grail of moral philosophy as it has been termed. But here we are no worse off than we are trying to convince the determined sceptic that the external world exists. I think, with Aristotle and the virtue ethicists, that we have reason to be moral: it is the best way to a fulfilled life, although luck, both good and bad, also plays a big part.


3 thoughts on “David Hume and the sensible knave

  1. The categorical imperative wouldn’t allow the egoist to form any maxim unless they could will to be a universal law. So I don’t think you could say an egoist could ever get around the problem of their maxims being irrational.

    1. Is the categorical imperative rational? I doubt even Kant would claim it was. The categorical imperative is a moral directive, not a rational one.

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