Introduction to Linguistics
The rules of a language, also called grammar, are learned as one acquires a language. These rules include phonology the sound system, morphology the structure of words, syntax, the combination of words into sentences, semantics, the ways in which sounds and meanings are related, and the lexicon, or mental dictionary of words. When you know a language you know words in that language sound units that are related to specific meanings. However, the sounds and meanings of words are arbitrary. For the most part, there is no relationship between the way a word is pronounced and its meaning.
Knowing a language encompasses this entire system, but this knowledge is different from behavior. You may know a language, but you may also choose to not speak it. Although you are not speaking the language, you still have the knowledge of it. However if you don't know a language you cannot speak it at all. There are two types of grammars descriptive and prescriptive. Descriptive grammars represent the unconscious knowledge of a language. English speakers, for example know that me likes apples is incorrect and I like apples is correct, although the speaker may not be able to explain why. Descriptive grammars do not teach the rules of a language, but rather describe rules that are already known. In contrast, prescriptive grammars dictate what a speaker's grammar should be and they include teaching grammars, which are written to help teach a foreign language.