Intellectual historians often make empirical claims, but can never know for certain if these claims are right. Uncertainty is thus inevitable for intellectual historians. But accepting uncertainty is not enough: we should also act on it, by trying to reduce and report it. We can reduce uncertainty by amassing valid data from different sources to weigh the strengths and weaknesses of competing explanations, rather than trying to "prove" an empirical claim by looking for evidence that fits it. Then we should report our degree of certainty in our claims. When we answer empirical questions in intellectual history, we are not telling our readers what happened: we are telling them how strong we think our evidence is-a crucial shift of emphasis. For intellectual historians, then, uncertainty is subjective, as discussed by Keynes and Collingwood; the paper thus explores three differences between subjective and objective uncertainty. Having outlined the theoretical basis of uncertainty, the paper then offers examples from actual research: Noel Malcolm's work shows how to reduce and report uncertainty about composition, and David Wootton's work shows how to reduce and report uncertainty about beliefs.
