Communication and Computation: New Questions About Compositionality
Shane Noah Steinert-Threlkeld

Abstract:
The topic of this dissertation is the famous principle of compositionality, stating that the meanings of complex expressions are determined by the meanings of their parts and how the parts are put together. The title belies its intent: rather than advancing a central thesis, it instead asks and provides answers to new questions about compositionality. In particular, these questions arise by shifting from viewing com- positionality as a property of symbolic systems -- where what I call 'status questions' are naturally discussed -- to viewing it from a procedural perspective, as operative in processes of production and interpretation. 
The questions the dissertation asks arise at successively narrower levels of scale. At the level of our species, I ask: why are natural languages compositional in the first place? At the level of small conversations: what role does compositionality play in the broader theory of communication? And at the level of an individual language speaker: what is the algorithmic interpretation of compositionality and what demands on complexity does it impose? In the pursuit of answers to these questions, a wide variety of methods are employed, from simulations of signaling games, to logic and formal semantics, to theoretical computer science, as appropriately called for.