Linguistic renderings of mental texts known as prefaces, which to a smaller or larger extent are the products of the genre schemes or prototypes, result from the cognitive activity of a concrete human being as a sender and presuppose a similar activity on the part of another human being, that is a receiver or receivers. In the process of creation and reception of a text, the language medium plays not only an epistemological role, that of understanding, preserving and ordering knowledge, but also that of transferring knowledge (communicative function) and creating a community. On the basis linguistic data contained in prefaces to specialist dictionaries, the present article attempts to understand the course of evolution taken by what is known as preface, from the text having the cognitive function as a dominant one to the text of a predominantly communicative function and of an increasingly different social function.