Mutual intelligibility is considered by some linguists to be the main criterion for determining whether varieties are separate languages or dialects of a single language, although others do not regard it as decisive, particularly when cultural factors interfere as they do with Chinese. As explains, linguists often ignore mutual intelligibility when varieties share intelligibility with a central variety (i.e. prestige variety, such as Standard Mandarin), as the issue requires some careful handling when mutual intelligibility is inconsistent with language identity. John DeFrancis argues that it is inappropriate to refer to Mandarin, Wu and so on as "dialects" because the mutual unintelligibility between them is too great. On the other hand, he also objects to considering them as separate languages, as it incorrectly implies a set of disruptive "religious, economic, political, and other differences" between speakers that exist, for example, between French Catholics and English Protestants in Canada, but not between speakers of Cantonese and Mandarin in China, owing to China's near-uninterrupted history of centralized government.