This volume investigates how phi-features—specifically person, number, and gender—function as a central nexus for collaboration across syntax, morphology, and semantics. The authors, Daniel Harbour, David Adger, and Susana Bejar, compile research that addresses the core questions and emergent directions of phi-theory. By integrating diverse methodologies, the text argues that these features provide a unique lens through which to observe the structure of grammar and the nature of linguistic interfaces.

Experts identify this volume as a foundational text for graduate-level research in theoretical linguistics. Readers frequently note the high academic density of the prose and the specialized nature of the arguments presented.