This paper deals with grammatical structures which are often used by native speakers of English even though they are on the verge of being unacceptable. Three sets of two examples are used to point to traditional grammatical rules being overriden in the domains of grammatical morphology (plural forming), lexical morphology (derivation), and morpho-syntax (aspect). Traditional grammars allow such structures, if at all, for communication purposes or for preserving the economy of language. The author believes such native speakers' 'errors' are possible due to the hierarchiacal internalized organization of grammatical rules. We use Grice's preference rules and basic notions of optimality theory to show that native speakers never break the rules of mental grammar. When confronted with two or more mutually contradictory rules in the same grammatical structure, they make intuitive sequential binary choices, and eventually comply with  the rule which is the highest in the hierarchy. The task of the modern grammarian would be to define this hierarchy.