He was appointed Professor of Linguistics at the University of California at Berkeley in 1966, where he worked for 30 years. While continuing his research on natural language processing, he began to focus on the evolutionary bases of language structure and language change. A paper he published in 1969 proposed a new theory of how language changes, called lexical diffusion. His team created the first linguistics database for some 20 Chinese dialects, which provided ample support for the theory of lexical diffusion. This theory has since received confirmation in many other languages, and the seminal paper has been cited well over 1,000 times, according to Google Scholar. His approach to research has always been multidisciplinary, having co-authored papers with leading geneticists, mathematicians, and psychologists.
In 1973, he was invited for a series of lectures at Peking University, which made him an Honorary Professor of the university in 2010. Also in 1973, he founded the Journal of Chinese Linguistics, and the journal celebrated its 50th anniversary last year. In 1992, the International Association of Chinese Linguistics was formed in Singapore, and he was elected Inaugural President. That same year, he was elected Academician of Academia Sinica, where he served as Chair of the Advisory Committee which helped create its Institute of Linguistics. Other prestigious honours he has received include: an award from the Guggenheim Foundation, Lifetime Achievement Award from the Anthropological Society of Shanghai, Honorary Degree of Doctor of Humane Letters from University of Chicago and Doctor of Humanities honoris causa from University of Macau, Honorary Professor from several universities, including Peking University, and Fellowship from the Linguistic Society of America. He has also held Resident Fellowships at advanced research institutes at Stanford, in Sweden, in Kyoto, and in Bellagio, Italy.
As a leading scholar in the linguistics field, he continues to have a substantial impact on the study of language and communication. In 2024, he received the Lifetime Achievement Award at PolyU’s inaugural Yuen Ren Chao Prize in Language Sciences for his distinguished contributions to the interdisciplinary studies in Chinese linguistics, evolutionary linguistics, and the cognitive neuroscience of language and ageing.