With respect to how comprehenders process presupposition and handle presupposition failure when verifying sentences, at least two hypotheses are possible: (1) presuppositions are treated like preconditions for evaluating the truth or falsity of a sentence, and are systematically verified before the assertion, and (2) presuppositions are 'backgrounded' and therefore taken for granted—meaning that assertions are systematically evaluated first. Three sentence-picture verification experiments are presented which suggest some version of the latter view; the results are compatible with there being no explicit step of presupposition verification. Instead, presupposition failure arises only accidentally, or in cases where the content of the presupposition is made especially salient in the discourse context by some external means.
"Processing presupposition: Verifying sentences with ‘only’,"
University of Pennsylvania Working Papers in Linguistics:
1, Article 17.
Available at: http://repository.upenn.edu/pwpl/vol14/iss1/17