  But the oddity of supposing that it is our understanding that justifies us in believing a self-evident proposition does not rest on the assumption that justification is to be defined as reason to believe, or that what gives us reason to believe that p is evidence for the truth of p or some benefit of believing this. If you ask someone why they believe some apparently self-evident proposition, such as that agony is bad, it would be very surprising if they replied by saying “I believe it because I understand it”.