Quantifying Dialect Mutual Intelligibility.

As students of language we were often asked: ‘How different are Chinese dialects?’ In the past, our standard answer to questions of this sort was to give a classification of the dialects. For example, we would say that Beijing belongs to Mandarin and Xiamen belongs to Southern Min. To a layman, that answer did not make much sense. So the follow-up question was usually the following: ‘Are they mutually intelligible?’ At that point, we were as lost as the layman. How could we talk about dialect similarity and mutual intelligibility?