This essay discusses three authors from the early seventeenth century (Galileo, Descartes, and Van Helmont) and the reasons that guided their decisions to write occasionally in their respective vernacular languages even though Latin remained the accepted language for learned communication. From their writings we can see that their choices were social, political, and always of high importance. The choice of language of these multilingual authors conveyed a message that was sometimes implicit, sometimes explicit. Their usage of both Latin and vernacular (...) proved, on the one hand, their place in the international learned community and, on the other hand, their interest and investment in changing the educational system. (shrink)