According to one view of linguistic information, a speaker can convey contextually new information in one of two ways: by asserting the content as new information; or by presupposing the content as given information which would then have to be accommodated. This distinction predicts that it is conversationally more appropriate to assert implausible information rather than presuppose it. A second view rejects the assumption that presuppositions are accommodated; instead, presuppositions are assimilated into asserted content and both are correspondingly open to (...) challenge. Under this view, we should not expect to find a difference in conversational appropriateness between asserting implausible information and presupposing it. To distinguish between these two views of linguistic information, we performed two self-paced reading experiments with an on-line stops-making-sense judgment. The results of the two experiments—using the presupposition triggers the and too—show that accommodation is inappropriate relative to non-presuppositional controls when the presupposed information is implausible but not when it is plausible. These results provide support for the first view of linguistic information: the contrast in implausible contexts can only be explained if there is a presupposition-assertion distinction and accommodation is a mechanism dedicated to reasoning about presuppositions. (shrink)