 Ambiguity would threaten this neat interdefinability. In the following section, we will explore whether there is an issue of concern here. The possibility of such ambiguity figures in work by Peter Downing on so-called “subjunctive” conditionals (Downing1959) and is explored subsequently as a more general problem in Wilson (1979), Goldstein et al. (2005), ch. 6, and later writers. The general argument, in brief, is that in some contexts there is a lack of reciprocity between necessary and sufficient conditions understood in a certain way, while in other situations the conditions do relate reciprocally to each other in the way required by the standard theory. If ambiguity is present, then there is no general conclusion that can safely be drawn about reciprocity, or lack of it, between necessary and sufficient conditions. Instead there will be a need to distinguish the sense of condition that is being invoked in a particular context. Without specification of meaning and context, it would also be wrong to make the general claim that sentences like “if p, q” are generally paraphrasable as “p only if q”. The philosophical literature contains numerous ways to make sense of the lack of reciprocity between the two kinds of conditions. Using a semi-formal argument, Carsten Held, for example, has suggested a way of explaining why necessary and sufficient conditions are not converses by making appeal to a version of truthmaker theory (Held 2016 – see Other Internet Resources). In what follows, the entry focuses on a rather different and possibly more widely accepted approach: the attempt to make sense of the lack of reciprocity in terms of the difference between inferential, evidential and explanatory uses of conditionals.