This paper focuses on modal adverbials in en/à la vérité (lit. « in/to the truth », meaning « to say the truth »). This variability (preposition en « in » or à « to ») is interesting because it does not appear for other adverbials with a seemingly parallel construction : en toute franchise, en un mot (« to be frank », « in a word »), etc. which do not present the same variability (*à toute franchise, etc.). The authors examine the emergence of en/à la vérité in the 15th to 17th centuries, and show that there is in part coexistence of those adverbials’ various uses ; in particular, textual and enunciative uses seem to appear simultaneously.