The seven (eight?) year old boy was talking to his mother on a Manhattan bus, which was slowly making its way down Columbus Avenue through thick traffic occasioned by the New York City Marathon. “It’s really trafficky,” said the mother. “‘Trafficky’ is not a word,” retorted the boy. “It’s a word if people understand it,” was the mother’s response, putting paid to the exchange and a quietus on her son.

In a sense, the little boy and his mother were both right. The American Heritage Dictionary of the English Language (4th ed., 2006) agrees with the boy (trafficky is unattested therein), but any non-juvenile native speaker of contemporary American English would agree with the mother.

Every linguistic utterance takes place in a communicative context defined by the speaker’s orientation and the latter’s associated function. When the orientation is toward establishing contact, the function is called phatic; when toward the content, referential; when toward the code, metalinguistic; when toward the addressee, conative; when toward the addresser, emotive; when toward the message, poetic.

For the boy, whose utterance was an exercise of the metalinguistic function, the judgment expressed thereby reflected a good command of the norm, i.e., of historically sanctioned usage, but only an incomplete, juvenile knowledge of the grammatical system that also countenances usage in statu nascendi. For the mother, by contrast, the internalized  system (of derivational morphology) was mature and, therefore, elastic enough to encompass everything functional that is productive in the language, including usage that exists in potentia.