This project relates the grammatical category of modality to human cognition and the mental representation of language: How are modal expressions mentally represented? We are interested in the linguistic knowledge that speakers of English have that allows them to choose between expressions such as “You should go home now”, “You have to go home now”, or “You ought to go home now”. These examples express non-factual ideas that are very similar, but subtly different. An idea that is still relatively widely held in the literature on modality is that the meanings of modal expressions can be distinguished on the basis of binary features such as the distinction between obligation and permission, “weak” and “strong” modality, and deontic and epistemic modality. While we do not dispute the usefulness of categorical semantic distinctions between different expressions of modality, we question whether these distinctions exhaustively capture speakers’ linguistic knowledge of modal expressions and whether matrices of cross-cutting categorical features adequately represent that knowledge. This project advances an alternative view that aligns itself with two recent theoretical developments in linguistics, namely the frameworks of Cognitive Construction Grammar (Goldberg 1995, 2006) and usage-based linguistics (Bybee & Hopper 2001, Bybee 2010). We hypothesize that knowledge of modal expressions is exemplar-based and probabilistic. In other words, speakers’ knowledge of modal expressions is not to be modeled as a paradigm of forms that can be fully described through a set of cross-cutting categorical features, but rather as a network of form-meaning pairs (Hilpert 2014, Hilpert & Diessel 2016) in which the forms of modal expressions are connected to a range of meanings through associative links. Differences in association strength account for the fact that speakers choose a certain modal expression in a certain speech situation. We thus view speakers’ knowledge of modal expression not as a discrete one-to-one mapping between a form and a list of semantic features, but rather as knowledge of the probability that a given form will convey a certain meaning in a certain context.