 A priori justification is a certain kind of justification often contrasted with empirical, or a posteriori, justification. Roughly speaking, a priori justification provides reasons for thinking a proposition is true that comes from merely understanding, or thinking about, that proposition. In contrast, a posteriori justification requires more than merely understanding a proposition. Observations based on our senses, or introspection about our current mental state, are needed for us to be empirically, or a posteriori, justified in believing that some proposition is true. Examples below bring out the contrast. The first proposition in each group is a prime candidate for being a priori justified, if justified at all, while the other propositions are prime candidates for being a posteriori justified, if justified at all. Some of the propositions are false, but that does not mean that we could not be justified in believing them before we had evidence that they are false.