He has been working on English phonology. His major interest is in the theoretical analysis of phonological patterns observed in a variety of English accents. The theoretical framework, Optimality Theory, has been adopted for his analysis of English accents. He made a theoretical contribution to phonological theory by proposing his own theory called the Lexicon-based Optimality Theory, which emphasizes the importance of lexical specifications in exploring phonological opacity seen in English phonology. He published a phonological textbook titled “English Phonology”(2016), which is useful for students at the graduate level. Currently He is endeavoring to widely spread the basics of English Linguistics to general audience whose linguistic knowledge is narrow and shallow. This effort led to the recent publication of “Understanding the basics of English Linguistics” (2021).