Noam chomsky has called the rules that we learn for making and interpreting sentences grammar.

Universal grammar, a term coined by Noam Chomsky, is a set of grammatical, or rather linguistic, rules that one is, bluntly said, born into. His theory suggests that humans are born with a certain innate knowledge of, or a genetic predisposition towards, the basic structural principles of their native language. This, along with knowledge acquired with time during their early childhood years, not by consciously or intentionally studying a language, but by listening conversations, and later on, engaging in them, is, according to Noam Chomsky, the reason why most of us speak our native language quite well, and mostly correctly in terms of grammar, long before we attend our first grammar lesson in school.