The Advantage of the Ungrammatical

Sentences with multiple complementizers like I told him that for sure that I would come often occur in speech and even in writing, although they are not generated by any formal grammar. Here we conducted an acceptability study and a self-paced reading experiment to test whether these 'Multiple That ' constructions are acceptable, and whether they are motivated by processing difficulty. Results showed that the presence of an extra complementizer always reduced the acceptability of sentences relative to single-complementizer versions, suggesting that this construction is not licensed by the grammar. However, the penalty incurred by the extra complementizer was smaller when more material intervened between the verb and the embedded clause, making integration costs high. In addition, reading times were faster on the embedded subject in Multiple That sentences compared to sentences with only one that in these more difficult sentences, suggesting that the extra that actually helps readers understand hard-to-process complement clauses. Multiple That need not be generated by the grammar under a theory of performance that allows processing pressures to add structures to the set of possible sentences.