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Word classes（词性概述）
1. Word classes（词性概述）
All words belong to categories called word classes (or parts of speech) ac-cording to the part they play in a sentence. The main word classes in English are:
• Noun（名词）
• Verb（动词）
• Adjective（形容词）
• Adverb（副词）
• Pronoun（代词）
• Preposition（介词）
• Conjunction（连词）
• Determiner（限定词）
• Exclamation（叹词）
Nouns, verbs, adjectives and adverbs are known as form classes (also known as content words or open classes)（形式类词，也叫做内容词或开放词，即所谓的实词）. While others are structure classes (also known as function words or closed classes)（结构类词，也叫做功能词或封闭词，即所谓的虚词）.
Probably the most striking difference between the form classes and the structure classes is characterized by their numbers. Of the half million or more words in English, the structure wordscan be counted in the hundreds（几百个）. The form classes, however, are large, open classes; new nouns and verbs and adjectives and adverbs regularly enter the language as new technology and new ideas require them.