Presuppositions are more persuasive than assertions if addressees accommodate them: Experimental evidence for philosophical reasoning

Best practice and descriptive research claim that presuppositions, such as the “too” in “,” increase the persuasiveness of arguments. Surprisingly, there is hardly any causal evidence for this claim. Therefore, we tested experimentally if advertisements and political statements with presuppositions are more persuasive than equivalent assertions. In 1999, Sbisà already theorized that “persuasive presuppositions” incidentally urge addressees to extend their (ideological) knowledge to make true the unstated assumptions writers have about what their addressee knows, which leads to greater agreement. Following Sbisà, we hypothesized that the persuasiveness depends on the addressee’s need and willingness to accommodate the presupposed content. In three experiments, we manipulated (a) the presupposition trigger using either the German additive particle auch “too,” the iterative particle wieder “again,” or factive verbs compared to assertive equivalents and (b) the preceding discourse context which supported the presupposition or not. Results show that presuppositions are perceived as more persuasive if they convey discourse-new information, largely irrespective of addressees’ ideological involvement.