R. examines the distribution of 'if' and 'when' clauses in written English, in order to determine what are the discourse factors that dictate their positioning vis-à-vis the main clause. It is argued that preposed `if' and `when' clauses are thematically associated to the preceding discourse as well as to the main clause, while postponed `if' and `when' clauses are only related to the main clause; and that preposed `when'clauses form an integral part of the narrative, helping to sequence the temporal contour of the mark narrative line, whereas postponed `when' clauses only function as added comments to the main clause.