Meaning and Use of Indefinite Expressions Paul Dekker Abstract: Sentences containing pronouns and indefinite noun phrases can be said to express open propositions, propositions which display gaps to be filled. This paper addresses the question what is the linguistic content of these expressions, what information they can be said to provide to a hearer, and in what sense the information of a speaker can be said to support their utterance. We present and motivate first order notions of content, update and support. The three notions are ach defined in a compositional fashion and brought together within a single and coherent framework.