The increase in frequency of the numeral construction  一 yī «one» + Classifier functioning as a marker of indefiniteness, observed in written Chinese in the first decades of the last century, is considered a product of the influence of the European languages. Actual data, however, seem to reject the hypothesis of a pure grammatical borrowing and demonstrate that the construction has undergone the full process of grammaticalization through which the numeral «one» has developed into the indefinite article in other languages. The function of the numeral construction in copulative sentences, where its increase has been particularly relevant, is here analyzed in order to understand what triggers its presence, being the choice of a bare NP always available in Chinese in these contexts. Data suggest that it is used when the speaker's stance is involved, a pragmatic feature at least partially shared by the indefinite article of some European languages.