MUTUAL INTELLIGIBILITY, WHICH SEEMS TO HAVE BEEN THE INITIAL BASIS FOR CHINESE DIALECT CLASSIFICATION, ALONG WITH GEOGRAPHIC PROXIMITY HAS PROVIDED A FAIRLY REALISTIC GROUPING OF THE MANDARIN DIALECTS. IT NOW SEEMS DESIRABLE TO WORK OUT A FORMAL DEFINITION IN PRECISE LINGUISTIC TERMS OF WHAT CONSTITUTES A MANDARIN DIALECT AND TO DISCOVER WHETHER THIS DEFINITION IS APPLICABLE TO ALL DIALECTS NOW CLASSIFIED AS MANDARIN, AND ALSO, WHETHER SUB-GROUPINGS WITHIN MANDARIN CAN BE MADE ACCORDING TO LINGUISTIC PRINCIPLES. ON THE BASIS OF THIS ANALYSIS, MANDARIN DIALECTS DO SEEM TO SHARE ONE DESCRIPTIVE FEATURE SHARED WITH NO OTHER NON-MANDARIN DIALECT AND TWO HISTORICAL FEATURES INVOLVING SOUNDS DEVELOPING FROM MIDDLE CHINESE. PUBLISHED IN THE JOURNAL OF THE CHINESE LANGUAGE TEACHERS ASSOCIATION, 1(3)/92-98, OCT. 1966. (NC)