Linguists classify the variations in spoken Chinese into seven (sometimes ten) groups, often called dialects. Within these groups, there are many subgroups, many of which are mutually unintelligible. Also the amount of "linguistic consciousness" varies between the groups. For example, a speaker of Cantonese dialect living in Hong Kong tends to feel a great deal of common identity with a speaker of Cantonese living in Taishan, even though these two varieties of Cantonese may be almost unintelligible. By contrast, a Wu speaker in Hangzhou generally does not think of themselves as belonging to the same group as a Shanghainese[?] speaker in Shanghai even though they are linguistically similar. One can see this even in the naming. The Hong Kong and Taishan person would both claim to be speaking Cantonese in the first case, while in the second case only the person from Shanghai would be speaking Shanghainese[?].
There are also great differences in the geographical variation of intelligibility. Mandarin dialects are remarkably constant with people living hundreds of kilometers from each other able to communicate intelligibly. In Fujian, people living ten kilometers away from each other can be speaking unintelligible variations of Min.
(The following three dialect groups are not always classified separately.)
In general, Chinese in southern China are fluent speakers of both Mandarin and the local dialect, but use a different variation based on the social situation. Mandarin is usually considered more formal and is required when speaking to a person who does not understand the local dialect. The local dialect is generally considered more intimate and is used among close family members and friends and in everyday conversation within the local area. Chinese speakers will frequently code switch between Mandarin and the local dialect. Parents will generally speak to their children in dialect, and the relationship between dialect and Mandarin appears to be stable.
Knowing the local dialect is of considerable social benefit and most Chinese who permanently move to a new area will attempt to pick up the local dialect. Learning a new dialect is usually done informally through a process of immersion and recognizing sound shifts. Typically, a speaker of one dialect of Chinese will need about a year of immersion to understand the local dialect and about three to five years to become fluent in speaking it. Because of the variety of dialects spoken, there are usually few formal methods for learning a local dialect.
Within the People's Republic of China there has been a strong official policy of not discouraging the use of local dialect or to imply that local dialect is inferior. On the other hand, in the Republic of China, the government had a policy until the mid-1980s of promoting Mandarin as high status and the local languages -- Taiwanese and Hakka -- as low status, a situation which caused a great deal of resentment and has produced somewhat of a backlash in the 1990s as part of the Taiwanese localization movement.
All dialects share a similar grammar system, different from the one employed by European languages. All words have only one grammatical form, as the language lacks conjugation, declension, or any inflection at all (there are minor exceptions). Concepts like plural or past tense are expressed in a syntactical way.
Tenses are indicated by adverbs of time ("yesterday", "later") and a particle (such as 了 le in Mandarin) indicating completion of an action or change of state (along with several other context-dependent meanings). Particles are also used to form questions; the syntax of a question is exactly the same as a declarative statement (basically Subject Verb Object) with only the appended particle, such as 嘛 or 嗎 (ma) in Mandarin, making it a question. Plural meaning has to be inferred from context, since the Chinese language doesn't provide any lexical means of expressing this concept for most nouns (apart from giving exact numbers).
Because of the lack of inflections, Chinese grammar may appear quite simple compared to that of the Romance languages to a speaker who is used to inflected languages. However, features which are unique to Chinese serve to make the grammar complex.
For example, Chinese has a complement of verb aspects different from anything to be found in Europe; Chinese distinguishes two perfectives, 了(-le) and 過 [过](-guo) which differ in nuance: the first signifies a recent relevent occurrence, such as "I have just gone to the store", and the other signifies a nonrecent occurrence that is relevent as an experience only, such as "I have gone to the store before." Chinese also uses a complex system of suffixes to distinguish the direction, possibility, and success of an action, so that the difference between "to search" and "to find" is grammatically realized in Chinese: 找(zhao3) for search and 找到 (zhao3dao4) for find (literally, to search and succeed). Finally, Chinese nouns require "counters" in order to be counted. Hence one must say 兩頭牛 [两头牛] "two heads of cows", not two cows, with 頭[头] "heads" being the "counter", or unit of measurement, or measure word. There are dozens, if not hundreds of counters in Chinese and these must be memorized individually for each noun. However, usage also depends on personal preference and dialects. For example, some people use 三部車 and others use 三台車 (three cars), with 部 and 台 being interchangable measure words.