Speech acts are intentional acts and as such lend themselves to philosophical analysis in terms of ends, means and the rules that govern them. Rationality involves norms of appropriateness of means for ends. Rationality considerations are, therefore, applicable to acts of language use. Some major linguistic phenomena are explained by such considerations.
The distinction between semantics and pragmatics is easier to apply than to explain. This might suggest that there is no one way of drawing the distinction and that how to draw it is merely a terminological question, a matter of arbitrary stipulation. In my view, though, these diverse formulations, despite their conflicts, all shed light on the distinction as it is commonly applied, in both linguistics and philosophy.