In a famous letter of 1709 to a young protégé, the third Earl of Shaftesbury commented at length on his philosophical differences with his own mentor, John Locke. Not only had Locke mistakenly attacked innateness, but he had also asserted, according to Shaftesbury, that virtue was measured by nothing more than fashion or custom. Right and wrong had no permanence as distinctions, no residence in the mind. Thus Locke had landed the ‘home blow’ aimed by Hobbes: Locke ‘struck at all fundamentals, threw all order and virtue out of the world’. The accuracy of these accusations can be debated, but the strength of Shaftesbury's reaction indicates the urgency and challenge of defining a philosophy of human nature in opposition to Locke, the man who had played a central role in Shaftesbury's education and upbringing.

The specific issues raised by Shaftesbury suggest that diversity played a key part in defining what he regarded as the pernicious effects of Locke's philosophy. Locke began with a critique of innate moral principles and the elimination of an innate idea of God in the first book of the Essay. In Book ii, Locke went further by introducing a sociological account of how moral rules functioned in practice – codified by Locke in the law of opinion or fashion – which introduced a perpetual disorder in the moral world in Shaftesbury's estimation.