The most common, and most purely linguistic, criterion is that of mutual intelligibility: two varieties are said to be dialects of the same language if being a speaker of one variety confers sufficient knowledge to understand and be understood by a speaker of the other; otherwise, they are said to be different languages. What is the term for when dialects A and B are mutually intelligible, dialect B and C are mutually intelligible, but dialects A and C are not mutually intelligible