One David Mortensen observes:
. . . language is a code employed only by code-breakers: that none of us knows the language we speak as a fully explicit system. Instead, we bluff our way through, filling in the gaps in our knowledge of the code with an inference here and a leap of logic there. This capacity to extrapolate from the known to the unknown is, in essense, grammar. . . .
(Cited by languagehat)