The object of this study are the syntactic and functional properties of extraposed vs. non-extraposed clauses in English (e.g. It is surprising that John went to London vs. That John went to London is surprising). The main emphasis is put on the differences of it-extraposition and non-extraposition in their discursive function. Kaltenbock shows that the exchangeability of the two structures as postulated by generative linguistics is to be qualified. Along with syntactic, semantic and stylistic aspects the work discusses mainly functional factors.