We are all intimately familiar with at least one language, yet few of us ever stop to consider what we know about it. The words of a language can be listed in a dictionary, but not all the sentences.
Speakers use a finite set of rules to produce and understand an infinite set of sentences. These rules comprise the grammar of a language. It includes the sound system and the way in which sounds and meanings are related.
This linguistic knowledge is, however, different from linguistic behavior. If you woke up one morning and decided to stop talking, you would still have the knowledge of your language.
Language is a tool of communication. But if language is defined merely as a system of communication, then language is not unique to humans. A basic property of human language is its creative aspect.
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虽然我们人人至少通晓一门语言，但很少有人会静心思考一下对语言了解什么。语言的词汇可以在词典中列出，但并非所有句子都能为词典所收入。
说话者可以运用一组数量有限的规则来表达与理解数量无限的句子。这些规则组成了语言的语法体系。语法包括音系以及语音和语义之间联系的规则。
然而，语言知识有别于语言行为。某天早晨你醒来后决定不说话，你仍然具有你所操
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语言的知识。
语言是交际的工具。但如果语言的定义仅仅是一种交际系统，那语言便不是人类的专有品。人类语言的一个基本属性是创造性。
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