Cross-linguistic generic categories like evidentiality, tense, aspect, number, and person are entrenched in linguistic theory. However, it is not clear whether there is much empirical substance to them. There is a remarkable lack of criteria for what counts as a category. This paper tries to show that semantic maps can be used to give empirical substance to claims about cross-linguistic generic categories. It is argued that, as falsifiable cross-linguistic generalizations, semantic maps provide us with a criterion for categorial status and category membership and also provide us with a basis for identifying relations between different categories. However, it is also argued that there are limits to the use of semantic maps in evaluating claims about cross-linguistic generic categories, and that the criterion for categorial status and category membership provided by semantic maps ultimately needs to be supplemented by other criteria. In its argumentation, this paper focuses on the category of evidentiality and on the relation between evidentiality and epistemic modality.