 Simon Blackburn (1986) argued that any realist attempt to explain why there is necessity in the world would fail because it faced a dilemma. Suppose we say that \(A\) is necessary because \(B\). \(B\) at least has to be true, but is \(B\) itself necessary? Blackburn thought we could not answer no, because to explain the necessity of a necessary truth \(A\) by appeal to a contingent truth would undermine the necessity of \(A\). But to answer yes is to invite regress, for now we need to explain the necessity of \(B\) by appeal to a necessary truth \(C\), and so on ad infinitum. Now, whether the contingency horn is indeed vicious is debatable (see Hale 2002 and Cameron 2010 for discussion), but focus on the regress involved in the necessity horn. Hale (2002) argues that the realist about necessity can resist getting into a vicious regress by distinguishing between transmissive and non-transmissive explanations of the necessity of any given proposition. Grant that the necessity of \(A\) can only be explained by a proposition, \(B\), that is itself necessary: that explanation will be transmissive if the necessity of \(B\) plays a role in explaining the necessity of \(A\), otherwise it will be non-transmissive. Hale (ibid., 308–309) offers as an example of a transmissive explanation of the necessity of \(A\) a proof of \(A\) with the necessary truth \(B\) as its sole premise. If \(A\) follows logically from a necessary truth, then \(A\) itself must be necessary. And in this case, the necessity of \(B\) plays a crucial role in the explanation, for if I do not know whether \(B\) is necessary, knowing that it entails \(A\) does not tell me whether \(A\) is necessary, for a contingent proposition can follow from another contingent proposition. In that case, \(A\)’s necessity seems to be hostage to \(B\)’s necessity, and so the ultimate explanation of \(A\)’s necessity will seemingly involve whatever explains \(B\)’s necessity, which is where Blackburn senses regress. But Hale thinks there can also be non-transmissive explanations of necessity. He suggests: ‘Necessarily the conjunction of two propositions \(A\) and \(B\) is true only if \(A\) is true and \(B\) is true’ because ‘conjunction just is that binary function of propositions which is true iff both its arguments are true’ (ibid., 312). While he grants that the explanans in this case is necessary, Hale thinks that its necessity is no part of the explanation. All that is needed to explain why it is necessary that \(A \amp B\) is true only if \(A\) and \(B\) are both true is the truth of the fact that conjunction just is that function which is true iff both its arguments are true. It may be necessary the conjunction is that function, but that is not part of the explanation of the original necessity, and thus the necessity of the explanans is not appealed to in a way that makes the success of the explanation dependent now on explaining this further necessity. Perhaps there is a new question to be asked concerning why this further claim is necessary, but our original explanation stands independently of whether we can successfully answer this new question.