How can we explain that understandings (intellectus) and sound understandings are formed or that expressions signify when there is no res subiecta that corresponds to them? Abelard discusses this question in various contexts relating to the formation of understandings, the signification of nouns, the problem of universals, and the formation of propositions. In all of them, the notion of attentio-attendere, Augustinian in origin, plays a crucial role. It orients Abelard towards an intentionalist semantics, which insists on the difference between the speaker's act of focusing on something (the modus attendendi) and this something as existing (the modus subsistendi), and away from a semantics based on the notion of similitude. I would like to show how all these analyses are connected, thereby showing the links between ontology, semantics, and psychology in Abelard's thought.