Throughout the final instalment of The Decline and Fall, then, Gibbon is repeatedly and variously made aware that philosophic historiography, for all its apparent critical acuity and sharpness of tone, is in fact a blunt instrument with which to dissect these centuries. It does not cut and display, but obscures by merely bruising and mangling.

It is the tenet of uniformitarianism which irreparably mars the edge of philosophic historical understanding. Uniformitarianism was not, of course, a belief confined to the philosophes. Chesterfield thought that a conviction of the uniformity of human nature was the sober knowledge which came with maturity; while Addison, writing of Chevy–Chase, commented incidentally and as if stating an indubitable truth that ‘Human nature is the same in all reasonable creatures.’ But there is the rub; what if you are dealing with people who in your terms are not ‘reasonable’? Would it be possible, after Hume's demystification of the idea of reason, to dismiss such people as irrational barbarians, thus reposing in the idea of a timeless and unchanging standard of reason of which your age was a perfect possession? Mrs Radcliffe, writing almost contemporarily with Gibbon, is sure not: