Ours is an uncertain world. Every choice we make, every decision we reach, is set against a background of massive ignorance about our past, our future, our circumstances, ourselves. This, ironically, is something that we know all too well.

Ignorance is ignorance of facts. It is a failure to know what is true. To know what is true, one must believe it (something that involves having a certain level or degree of confidence in it) and do so with adequate justification. Thus ignorance can come about in one of two ways: either by way of failure to believe the truth or by way of believing it without adequate justification. There are two corresponding kinds of uncertainty: doxastic uncertainty, which consists in one's lacking full confidence in a proposition, and epistemic uncertainty, which consists in one's lacking justification in having full confidence in a proposition. Although not all uncertainty entails ignorance – one can know a proposition regarding which one is either not fully confident or not justified in being fully confident – all ignorance entails uncertainty of one or both kinds.

Philosophers are divided on the moral significance of the ignorance that besets us. Some say that it has a direct impact on how we ought to behave; others deny this, claiming that it only affects how we ought to be judged in light of the behavior in which we choose to engage. Until recently, I sided with the latter. I now side with the former.