Removing the Blades from Hume’s Guillotine

by Tauriq Moosa

David-Hume-Scotland-17111776-289536 Hume’s Guillotine: “One cannot derive an “ought” from an “is”. This thesis, which comes from a famous passage in Hume's Treatise [says]: there is a class of statements of fact which is logically distinct from a class of statements of value. No set of statements of fact by themselves entails any statement of value. Put in more contemporary terminology, no set of descriptive statements can entail an evaluative statement without the addition of at least one evaluative premise. To believe otherwise is to commit what has been called the naturalistic fallacy.”

– John Searle, ‘How to Derive an “Ought” from an “Is”’, The Philosophical Review, 1964

Beware, people. This is a long piece. Even I’m uncertain about it. Here we go then.


Major ethicists like Immanuel Kant and indeed – to an extent – Thomas Aquinas sought to establish a rational basis for deriving moral considerations. Why rationality above other justifications? Consider: one and one is two. This is a statement that appears to hold true regardless of the state of the world, whether we’re dreaming or awake (as Descartes famously pointed out in his Meditations), whether we’re in pain, and so on. However there is an implicit assumption being made here, too: that if we do agree that one and one is two, we who agree to this statement are rational agents; that is, beings who accept the constraints and rules of logic and rationality.

This appears to only beg the question: Why should anyone accept that one and one is two? (This problem so vexed the young Bertrand Russell, that he nearly mentally destroyed himself as an adult trying to establish conclusively that one and one is two.) As Sam Harris has said, how do you convince a person not interested in rationality to use rationality? As soon as you start making rational arguments, you’ve already lost.

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