The existence of prepositional variation in constructions such as speak about/of something can be motivated semantically in that about and of invite different construals of the topic they introduce. This article reports on a study carried out to test the hypothesis that the semantic distinction is reflected in the length of the object which complements the preposi- tion. The results suggest that object length might indeed play a part in the choice between about and of. The study also reveals additional factors which might influence speakers' choice of the topic-introducing preposition.