Because (of) is ambiguous between a `reason' and a `plain cause' interpretation. Presenting a semantic analysis within the framework of Discourse Representation Theory, I argue that because (of) always denotes a causal relation between causing facts and caused entites of various sorts and that its interpretational variance is dependent on the ontological nature of the caused entity. Finally, I point to a difference between sentential-complement because and nominal-complement because of with regard to their interaction with modals. Whereas both because and because of may outscope e.g. deontic necessity modals, only because may outscope epistemic modal operators.