Why is the Min Nan spoken in Fujian almost identical to the Min Nan spoken in Taiwan, but incomprehensible to the Min Nan spoken in Hainan?
There a very good explanation to this because the people who settled in Taiwan were originally from Quanzhou and Zhangzhou. The reason why Hainanese is so far off from Hokkien is because they never settled there. In my opinion labelling Hainanese as Min Nan is a bit a misnomer because it doesn follow the historical migration pattern that developed the language. The aboriginals of Hainan are actually the Li and Yao. The first Han Chinese to settle the area were people from Guangxi and Guangdong province so they most likely would have spoken some variant of Cantonese a long time ago. Around the fall of the Song Dynasty you started seeing migrants from Xinghua prefecture in Fujian. This area is the central cost of Fujian and they speak a different branch of Min language called Puxian Min. The new migrants pushed the older migrants into more impoverished areas thus the new language of these new migrants became the prestige language for Han Chinese. Genetically most of the Han Chinese inhabitants are closer to the people in Guangxi and Guangdong. So you have this mix of people from Guangxi and Guangdong with their influences and the original natives (Li Yao) mostly likely have some influence on the original Puxian language from the migrants that came during the fall of the Song Dynasty. Hainan people - Wikipedia s This map shows a more accurate visualization of Min languages; however I would probably separate Teochew from Hokkien because for the same reasons why Hainanese and Leizhounese are on the map is actually more closely related to Puxian Min. So in general Hainanese and Leizhounese are grouped together as Qiong-Lei a subgroup since these two languages are much closer to each other. If you go by Li Rong classification which the map above is based on you have Hainanese and Leizhounese separated from Minnan. With Hainanese you are going to find that a lot of their vocabulary is highly influenced by the other groups that reside on the island such as the Li and Yao therefore the vocabulary and the stem the roots of these words are going to different. In the map you can also see the location of Putian which is in the teal region. Notice that it squeezed in between the light blue (Minnan) and light green (Min Dong). So the question what is Putian (Puxian) and how does it relate to Minnan? Well in a very distant past they both came from Proto Minnan before splitting off. Proto-Putian (Proto-Puxian) would later influence modern Putian which they call Hing Hua Teochew Leizhou and Hainanese. There is a very distant relationship; however Puxian is also highly influenced by Min Dong languages like Fuzhounese. If we think about this as a language continuum you can see why since it in between two other branches of Min languages. A lot of linguist separate Puxian from both Minnan and Min Dong. Because were looking at a continuum Puxian will have more cognates with the Quanzhou dialect of Hokkien. Which is interesting because Teochew which has been grouped with Minnan actually has more cognates with the Zhangzhou dialect of Hokkien. If you look at the diagram above Teochew (Chaozhou) stems from Proto-Putian. Pu-Xian Min - Wikipedia s The other thing that makes Hainanese so different is the fact that there been a fairly significant sound shift from Minnan language. Leizhounese may share a lot of the same cognate (the same root from where their vocabularyes from) but phonology has shifted considerably enough that it seems like it an entirely different language. *The phonological system of Hainanese corresponds well with that of Hokkien but it has had some restructuring. In particular etymological *anterior stops have undergone implosivization (*p u253 *t u257 etymological *aspirated stops have spirantized (*pu2b f *tu2b h *cu2b u255 *ku2b x) and etymological *s have hardened into stops (*s t) and *h u266. Additionally some dialects have u261 s and u291 is allophonic with *From this source Hainanese - Wikipedia s So to kind of sum it up Hainanese is actually closer to Puxian Min but theyve gone through a lot of transformations which includes sound shifts. Their cognates are much closer to Puxian Min too but it even closer whenpared to Leizhounese. The reason why Hainanese has been tied to Minnan has to do with a distant past when they were once the same language Proto-Minnan. It still part of the same linguistic continuum but really they are part of a sub-branch. It related not exactly about Hainanese but this gives an explanation of Leizhounese and at the end a tiny bit about Hainanese. Origin of Leizhou Min language