This paper addresses a yawning gap in IS theory and practice. In the information systems (IS) discipline and profession, the concept of authentication is commonly limited in scope to the checking of assertions relating to identity. The effective conduct of organised activities depends on the authentication of not only assertions of those kinds, but also many other categories of assertion. The paper declares its metatheoretic assumptions, and outlines a pragmatic metatheoretic model whose purpose is to establish a workable framework for IS practitioners, and for researchers oriented to IS practice. Within this frame, a generic theory of authentication is proposed, encompassing not only commonly discussed kinds of assertions, but also other important categories relating to real-world properties, asset-value and content-integrity. This surfaces unaddressed opportunities for IS researchers in content-integrity authentication at the semantic level, relating to assertions of fact.