This article investigates the omission of the that-complementizer in extraposed subject clauses (e.g. It is obvious (that) she did it), which has so far received very little attention in the literature. Using corpus data from the British component of the International Corpus of English (ICE-GB) various potential conditioning factors are analysed. Of these the following are found to have a major impact on the choice of zero that: informality of the text category, type of matrix predicate, and information value of the complement clause. On the basis of these corpus results the article then proposes a unified explanation for the use of that or zero by positing an underlying abstract feature of ‘distance’; for the that-complementizer, a semantic residue of its original demonstrative use, which gives rise to different pragmatic interpretations, depending on the actual use of that in context.