Special attention should be paid to end users when drafting subtitles for the deaf and hard of hearing. Understanding the metalinguistic knowledge of deaf people, whose language has no written form, is a much needed point of departure when devising subtitles, so that the exercise becomes worthwhile for those whose first language has no fixed or standardized written representation. This paper revises the concept used in linguistic historiography, namely grammatisation (Auroux, 1994), to explain the role played by the appearance, consolidation and democratization of writing as an instrument for the development of an objective knowledge of language, with important practical consequences for the standardization of languages.