If one compares the account of the grammaticalization of the indefinite article with the account of the grammaticalization of the definite article in the same language – here, in English and in Spanish –, a high degree of analogy strikes the eye. Although the definite and the indefinite articles stem from entirely distinct sources, viz. the demonstrative subsystem and the numeral subsystem, resp., they converge to form a solid and homogeneous paradigm of their own. The two articles occupy the same syntagmatic position and are in a binary opposition in this position. This process is called paradigmaticization. A singular individual concrete noun phrase by default starts with a determiner, where the article steps in if no more specific determiner is used. In other words, the article has reached a considerable degree of obligatoriness.

To the extent that the article is obligatory, it carries no information. At the same time, it has a fixed position. While the numeral ‘one’ and the demonstrative determiner in Latin had free word order in front of, after or even inside the nominal group, the Spanish article occurs at the start of the noun phrase. Analogous considerations apply to the English indefinite article. Syntagmatic variability shrinks to the point of fixation. Thus, the article signals that what follows is a noun phrase; and if it is obligatory, this is the only information that it provides. This is a purely structural function. It has two theoretical aspects:

• This kind of meaning, if meaning it be called, has been called the metalinguistic function of grammatical formatives: They may be said to impart information, but not information on the world designated, but on the expressions making up the message.
• If the formative signals a component of grammatical structure, it contributes to structuring the message. It may be redundant from the point of view of the content of the message, but it supports fluent production and understanding.