The title of this lecture raises two questions. The first is who are the "simple folk" it refers to, and why is the phrase in quotation marks? The second is what would make it possible to assume that medieval literature was aimed more at the "simple folk" than that of any other period, and to determine how medieval literary art would take the simple folk into account - an assumption that is not self-evident, given how intellectually and socially elitist the intellectual and literary world of the Middle Ages appears to have been.
"Les simples gens" is an Old and Middle French expression, hence the quotation marks. It refers to simple minds, devoid of intellectual knowledge and training, generally in a religious context and without any pejorative connotation. It is often used in the pedagogical context of religious instruction and pastoral care. A late 14th-century French treatise entitled Le Doctrinal aux simples gens is a compendium of doctrinal knowledge that a parish priest should teach his parishioners.
The starting proposition of the lecture is that the desire or need to speak to "simple folk" would have had an effect on literary expression in the Middle Ages. Whether this is true of preaching to the people or of edification literature is easy to guess - so easy, in fact, that the question is of limited interest. That it is true in general would be more interesting, but seems more dubious in the case of a literature that constantly displays its contempt for the vilain, and whose Latin side is so infatuated with the model of classical Latinity. It seems absurd to look for a literary art that is oriented towards the simple. And yet, this literary art does exist, the fruit of constraints that were exerted not only in the pastoral sphere, but also of aesthetic choices whose interpretation is ambiguous, but whose existence is indisputable.