Principle (C′) is considerably less bold than principle (C). This can be seen if we reflect on what would count as a counterexample to (C). Consider a case in which a person knows perfectly well that he has just taken some hallucinogenic drugs. Suppose he knows the typical effects of these drugs. Suppose he has good reason to believe that there are no unicorns, but now he believes that he is perceiving something to be a unicorn.