 To conclude this section we outline an explanation of epistemic transmission failure delivered by Smith  (2009),[8]  which is very different from all those considered so far. According to Smith, epistemic justification requires reliability. A subject s’s belief that p, held on the basis of s’s belief that e, is reliable in the sense defined by Smith if and only if in all possible worlds including e as true and that are as normal (from the perspective of the actual world) as the truth of e permits, p is also true. Consider Zebra again. s’s belief that P3 — that the animals in the pen are zebras — proves reliable in Smith’s sense when it is based on s’s belief that E3 — that the animals in the pen look like zebras. (Disguising mules so as to make them look like zebras is after all an abnormal practice.) Thus, all possible E3-worlds that are as normal as the truth of E3 permits are not worlds in which the animals in the pen are cleverly disguised mules. Rather, they are P3-worlds—that is to say, worlds in which the animals in the pen are zebras.