[1] His research focuses on language acquisition, variation and change, and is carried out from a broadly Chomskyan perspective.
His first book, Knowledge and Learning in Natural Language (2002), proposes a model of syntactic acquisition couched within the Principles and Parameters framework.
The model is applied to a number of case studies in language acquisition and historical linguistics.
Yang's third book, The Price of Productivity: How Children Learn to Break the Rules of Language (2016), won the Linguistic Society of America's Leonard Bloomfield Award.
[2] This book deals with the acquisition of linguistic rules with exceptions, and proposes a quantifiable upper bound on the number of lexical exceptions that a grammatical rule can tolerate.