Abstract: Competence is a key concept of modern linguistics. This article seeks to explain how one of its incarnations, that is, communicative competence, can be applied to historical sociolinguistics for which the sources are often sparse and deficient. Even if written documents convey only an incomplete picture of the linguistic knowledge of their writer, this particular case study is an attempt to reconstruct the linguistic profile of a French soldier with modest literacy skills in the context of production during the First World War.
