This article examines the history of a construction type which has been almost completely disregarded in the extensive literature on complementation, namely declarative complement clauses introduced by if and though. Contrary to the standard view, which favours an adverbial analysis for these clauses, it is shown here that there are convincing arguments for considering certain if- and though-clauses as complements, though it is also admitted that their behaviour differs in some respects from standard cases of declarative complementation. The article also reveals the existence of a number of factors favouring the selection of the minor complementizers if and though over the major complement-clause links that and zero in Old, Middle, and Early Modern English. Evidence has primarily been drawn from the diachronic part of the Helsinki Corpus of English Texts.