Grammar has several meanings, from the technical to the everyday. In its most popular sense, a 'grammar' may be little more than a list of rules, handed down by some authority, which supplies advice on how to speak 'correctly'. Others may think of 'grammar' as a set of another type of rules, ones which state as simply as possible how words are formed and arranged in sentences. For the linguist, on the other hand, what might come most immediately to mind would be a highly technical, abstract and theoretical account of the system of language itself.
The first use of the term represents a prescriptivist view, and is often to be found as advice in newspapers and in manuals of style. Journalists, teachers, and other people who work with language on a daily basis, as well as self-appointed authorities, may all offer recommendations from time to time about what is standard and non-standard. The linguistic validity of some of these 'rules' may be disputed, either by competing authorities, or by linguists pointing to apparent counter-evidence. Linguists usually work with a descriptive work of language, declining to tell people how they should speak or write, but instead recording their usage and compiling this evidence to support their claims about the nature of language.
The idea that 'grammar' can be reduced to a set of straightforward 'rules', such as "pluralise an English noun by adding -s to the end", is a view that may appeal to educators who wish to put across the most fundamental aspects of a language's grammar in as simple a way as possible. Again, linguists reject this definition, as native speakers are intuitively aware of many exceptions to any proposed 'rule', and their understanding and production of language implies the use of a highly complex, structured system which can neither be easily described nor reduced to a learnable list. "All grammars leak."
- Edward Sapir (1921), Language: An Introduction to the Study of Speech.