In inflected languages, form classes and their relations in a sentence can often be told from overt markers such as endings for plural nouns or tense forms of verbs. To a very limited extent Chinese also has overt markers, such as -tz for nouns, -le for verbs, but in most cases the total grammatical behavior of form classes is not revealed except in certain frames; otherwise it remains implicit, or covert. We shall cite two sets of examples, one in English and one in Chinese, as they form very similar covert categories. Of substantives in English, the names of countries and cities form a covert class in that one cannot use ‘it’ or ‘her’ after the prepositions ‘in, at, to, and from’. Thus, one can say ‘That is a large house. He lives in it.’ But after ‘That is San Francisco.’, one cannot say ‘He lives in it.’, but must say ‘He lives there.’ Similarly, the substantives 上海 Shanqhae ‘Shanghai’, 王家 Wang .jia ‘the Wangs’(house)’, 桌子 juotz ‘table’, and 你 nii ‘you’ seem to be all alike, but when preceded by 到 daw ‘goes to’, the noun juotz and the pronoun nii must be suffixed by the localizer 那儿-.nail to form place words before they can be objects of the preposition daw, thus: 这是上海，我喜欢上海，我到上海去。那是王 家，我喜欢王家，我到王家去。Jeh sh Shanqhae, woo shii. huan Shanqhae, woo daw Shanqhae chiuh. Nah sh Wang. jia, woo shii. huan Wang. jia, woo daw Wang.jia chiuh. ‘This is Shanghai, I like Shanghai, I go to Shanghai. That is the Wangs’ (house), I like the Wangs, I go to the Wangs.’ But, with common nouns and pronouns, we have这是摇椅，我喜欢摇椅，我到摇椅那儿去。那是你， 我喜欢你，我到你那儿去。Jeh sh yauyii, woo shii. huan yauyii, woo daw yauyii- .nall chiuh. Nah sh nii, woo shii. huan nii, woo daw nii .nail chiuh . ‘This is a rocking chair, I like rocking chairs, I go to the rocking chair. That is you, I like you, I go to you.’ Thus, the distinction between place words and nouns, like most other grammatical categories in Chinese is a covert and not an overt one.
 Chao Y R. A grammar of spoken Chinese[M]. Univ of California Press, 1965.