It is ironic, however, that Hume himself, in the 'is-ought' passage (contained in his 1739 A Treatise of Human Nature)6, was summarising his argument against the 'rationalists' and for passion as the basis of morality. For Hume, reason alone is insufficient to motivate the will; he concludes that: '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.' This is not a conclusion based on philosophising, but one founded on observation of human nature.
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