This paper studies the evolution in French of the modal adverbs voirement and vraiment, from Old French to the 17th century. Both adverbs make a comment on the degree of truth of the utterance as perceived by the speaker. They take an utterance p into their scope and reinforce its degree of truth and certitude. Voirement marks agreement, it points backwards and repeats literally or reformulates what has been previously said. In dialogue it may be polyphonic: it refers to a point of view which, on reflection, is confirmed. In spite of an evident link between them, vraiment has never had a polyphonic or confirmative function. Unlike voirement, it can appear in a context of disagreement. More strongly assertive than voirement, vraiment is not retroactive. In vraiment p, the speaker asserts emphatically the truth of an utterance p on the basis of his personal conviction.