Painted in 1759, William Hogarth's Sigismunda illustrates a story in Boccaccio's Decameron about a woman grieving for her husband. Fighting back the tears and wearing copious jewellery, she clutches a gold vase containing the heart. The critics were unimpressed. Connoisseur Horace Walpole called Sigismunda "a maudlin whore".

Hogarth was the master of the satirical, the low; a painter of 18th-century London life whose images still gnaw at the imagination. But he wanted more. He wanted to be recognised as a painter of grand themes like the old masters.

Tate Britain has stepped in to rescue Sigismunda, to put the painting in context and argue that it was Sigismunda's overt sexuality that offended men like Walpole. The trouble is that the other works displayed as evidence are far more imaginative. The mistake was to show The Lady's Last Stake (1759). In this comic masterpiece, a woman in a green-wallpapered drawing room has been losing at cards to her beau and is now reduced to her last stake: her body. Cards burn in the hearth, and a clock on the mantelpiece portrays Time with a scythe.

There's a buoyancy to this painting that lifts it off the wall. Apparently, a rich art lover saw it and offered Hogarth a huge sum for something similar. Wilfully, Hogarth painted Sigismunda. Grosvenor was appalled. And who can blame him?

There's plenty of subversion in Hogarth's paintings and prints without having to overanalyse such a minor work. What Tate Britain should do is put on an exhibition celebrating his comic genius, instead of assuming - with a perversity as great as that which prompted Sigismunda - that because something is excluded from the canon it must be interesting. Sometimes works of art fail not because they are threatening to the social order but because they are bad.

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