Idioms, collocations, and structure: Syntactic constraints on conventionalized expressions

Phrasal idioms have been used as evidence in syntactic theorizing for decades. A common assumption, occasionally made explicit (e.g., Larson 2017 ), is that non-literal phrasal idioms differ significantly from completely literal collocations in the kinds of syntactic structures they can be built from. I show with a detailed empirical study that this is false. In fact, the syntactic constraints on idioms and collocations are identical . In particular, patterns that are missing from one are missing from the other, most strikingly ditransitives with a fixed first object and open second object (* throw the wolves X ). Idioms and collocations should therefore be treated the same, as a broad class of conventionalized expressions . I propose a new analysis of the syntactic forms that conventionalized expressions can take. Unlike most previous analyses, I take the open slots to be part of the expression, and the task then becomes to explain the distribution of the open slots. A structural constraint on open slots accounts for the missing ditransitive pattern. It also explains why expressions with a fixed subject but open object are rare, but also why certain examples of this pattern do exist in English and in other languages.