(Source: An Introduction to Language by Victoria Fromkin and Robert Rodman, 6th Ed.)
Part One: Introduction to Linguistics
Every human knows at least one language, spoken or signed. Linguistics is the science of language, including the sounds, words, and grammar rules. Words in languages are finite, but sentences are not. It is this creative aspect of human language that sets it apart from animal languages, which are essentially responses to stimuli.
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, i.e. 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 (or signed) and its meaning. [Learn more]