In the literature on nominal tautologies, it is assumed that common knowledge is a crucial ingredient for their interpretation. This paper explores a different approach: we argue that invoking shared knowledge is at the same time too strict and too vague as a condition for the understanding of tautologies in context. More specifically, we claim that, on the one hand, the hearer's previous knowledge about some specific set of properties of the entity referred to in the tautology is not always necessary: lack of previous knowledge can be repaired by accommodating new assumptions or compensated by providing additional explicit content in discourse. On the other hand, the hearer's previous knowledge about some specific set of properties of the entity referred to in the tautology is not always sufficient: only permanent, classificatory properties can be evoked by a tautology; transitory states, by contrast, are systematically rejected, even if they constitute shared knowledge and are supported by the context. We provide evidence for our claims both from the corpus study, analysing examples of tautologies with proper names from COCA and web-based sources, and experimental study designed as a verification task, additionally measuring reaction times for replying to a given question.