On the syntactic status of I 'm sure

Abstract

This study tests whether the syntactic status of the subject–adjective combination I’m/I am sure is similar to the subject–verb combination I think (i.e., whether it exhibits the same signs of grammaticalisation along two different parameters). More specifically, the study is concerned with the ability of I’m/I am sure to (i) occur in clause-medial and clause-final position, and with (ii) its preference for that-omission, by comparing the behaviour of I’m/I am sure with the results reported for I think in previous studies. The results show that I’m/I am sure behaves in a similar way to I think both in terms of its ability to occur in clause-medial and clause-final position, and in terms of its preference for that-omission. However, sure is both much less frequent than think in general, and is also proportionally less dominant among the class of adjectival predicates followed by that-clauses than think is among verbal predicates. This makes it difficult to argue that they have developed independently through the same frequency correlation. Instead, I argue that sure and think are part of the same grammaticalised constructional schema, and that the frequency of think could be seen to have an impact on the grammatical status of the parallel construction with sure.