One theory about how dialects came into being suggests that it was Northern Chinese who passed on the language to the South, which blended it with local speech.

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There has been general agreement on the categorization of Chinese dialects since the Language Atlas of China was jointly compiled by the Chinese Academy of Social Sciences and Australian Academy of the Humanities, in 1987.

In general, Chinese dialects are divided into Mandarin Chinese and non-Mandarin Chinese. Mandarin has the most speakers as the speaking region spreads from Northeast China to the Southwest.

But here, Mandarin is not exactly Putonghua, or standard Chinese, which is the common language (with standardized pronunciation and grammar based mainly on the Beijing dialect) and is used on official occasions, in the media and during inter-regional communications.

Within Mandarin, there are about eight dialect regions, including Beijing, Northeast China and Hebei-Shandong. Most of these dialect regions are in the North. That's why Mandarin is often referred to as Northern dialect.

But exceptions include Jianghuai Mandarin and Southwest Mandarin. The former covers most of the regions on the north bank of the Yangtze River in Jiangsu and Anhui provinces. The latter regions refer to Sichuan, Yunnan and Guizhou provinces.

One of the reasons these dialects are categorized as Mandarin, though they vary a lot in intonation, is that they share similar pronunciation and grammatical rules, and thus are generally mutually intelligible.

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By contrast, there's a lot more complications in the non-Mandarin section, which is more widely known as the Southern dialects spoken across mainly in the South and East China.

Senior dialect researcher Li Lan at the Chinese Academy of Social Sciences says after the 1980s scholars generally agreed that non-Mandarin has nine different dialects that vary from each other in pronunciation, grammar and vocabulary and are thus basically mutually unintelligible.

Among them, the most prominent are the Wu, Yue (Cantonese) and Min dialects, which are, respectively, spoken by people in Shanghai-Jiangsu-Zhejiang, Guangdong-Hong Kong and Fujian-Taiwan.

Wu, with around 70 million speakers, is China's most widely spoken non-Mandarin dialect. Cantonese ranks second with some 60 million speakers in the country. But Li says, worldwide, it tops the ranking with more than 10 million additional speakers overseas.

These dialects have commonalities in a linguistic sense, but it doesn't necessarily mean people within the same dialect region can smoothly talk to each other.

Quite often in Zhejiang and Fujian provinces, residents in neighboring villages have problems understanding each other and sometimes even within a village.

Geographical division, like rivers and mountains, are part of the reason, Li says. But, more importantly, frequent immigration provides the means for people who tend to speak dialect to be influenced by their native dialects. From this point of view, Li says, China could have at least 200 dialects.

The differences between these dialects are no less obvious than that between some European languages, such as German and Dutch, Li says. That's why he says the distinction between the definitions of language and dialect is often vague.

The one key factor making Chinese dialects remain variants of a unified language is that they basically use the same characters.

More importantly, due to frequent inter-regional interactions, dialects are mutually influential and hard to recognize.

"These dialects are bound to be subject to continuous change in the future," Li says.

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