One large experiment is reported which examined the role of geometry and functional relations on the comprehension of the spatial prepositions over, under, above and below. The task consisted of rating how appropriate a sentence (containing one of these repositions) was to describe a picture. The results show a significant effect of functional relations on the ratings given, demonstrating the importance of functional relations as a determinant of the comprehension of spatial prepositions. However, while over and under were very sensitive to functional relations, above and below were more influenced by geometric relations. Thus these results indicate for the first time that spatial prepositions are differentially influenced by geometric and functional relations, and that geometry and functional relations are distinct factors.