This introduction develops a concept of epistemology as the study of forms of knowledge. There must be clarity about these forms before one can address the questions of the validity and limits of knowledge. However, the concept and the individual forms of knowledge—perception, memory, experience, science, etc.—cannot be clarified through definitions, but only through an analysis of the usage of the respective terms. Thus, this introduction primarily serves as a contribution to the grammar of epistemic expressions. It does not stop at description; rather, it critically examines those usages for problematic assumptions and misleading metaphors—and it always discusses alternatives. References to the problems of the validity and reality of knowledge complement the concept outlined here.