It is not always clear what counts as a good middle sentence in English. Whereas examples like 'This book reads well' or 'Roald Dahl translates easily' seem to be readily acceptable, the same cannot be said of others like 'This book reads' or 'French acquires easily'. This book offers a comprehensive account of the English middle construction and the restrictions on its formation.

Based on a careful analysis of the semantic idiosyncrasy and the grammatical properties of the construction, the author investigates the manner in which middles are spreading and shows that not all new middles exhibit the same degree of acceptability. A number of constraints are identified as being responsible for this gradience. The extent to which each of them affects middle acceptability and the way in which they interact with one another is investigated, leading to an amendment of some of the existing proposals regarding the issue of what a middle sentence can or cannot be. The analysis relies on a substantial amount of data obtained by eliciting acceptability judgements from native speakers, on a theory of gradient acceptability, and on a consideration of aspects of language use and sentence-processing, and not of language-internal aspects only.