 There are a variety of views about whether a priori justification requires some sort of evidence or whether, instead, some propositions can be “default reasonable”, or that a person can be entitled to accept certain propositions independent of any evidence, perhaps because they are reasonable presuppositions of some area of inquiry. Philosophers who think that a priori justification requires evidence differ about the details. Some think that a priori evidence can be defeated (overridden or undercut) by other evidence, including evidence from sensory observations. There are a variety of views about whether a priori justification, and knowledge, must be only of propositions about what is possible or necessary, and if necessary, only of analytic propositions, that is, propositions that are in some sense “true in virtue of their meaning” (as in examples  1a–8a,  below). Those who think that a priori justification requires evidence often think that the evidence is provided by rational intuitions or insights, but there is disagreement about the nature of those intuitions or insights, and critics deny that they really do constitute evidence.