We need to be particularly suspicious of politicians and other public figures who invoke high moral principles to explain their own behaviour. Such, at least, is the view of the most hard-headed of our historians. It is safe to assume, they tell us, that such professed ideals will be ex post facto rationalisations, and that the actions of such dubious characters will generally be undertaken for motives of a very different and often inadmissible kind. Among recent historians, Sir Lewis Namier has perhaps been the most influential proponent of this vision of politics, although it is ironic that his arguments in defence of his position often sound very like those of the Marxist historians whom he always professed to despise. Like many Marxists, Namier was committed to two connected claims about the interplay of principle and practice in public life. The first is that we are indeed justified in dismissing the ideals professed by politicians as so many attempts to invest their conduct with what Namier liked to describe as a spurious air of morality and rationality. The second is that it follows from this that such principles play no causal role in bringing about their actions, and do not therefore need to figure in our explanations of their behaviour. As Namier summarised, ‘party names and cant’ are mere epiphenomena, providing us with no guide at all to the actual motives and underlying realities of social and political life.