The structure of a medieval quaestio, e.g. each article in the Summa Theologiae
(1) The posing of the question
(2) Objections to the position that the master (magister) will ultimately defend
(3) The sed contra: most often a brief Scripture quote or passage from a Father of the Church suggesting the position that the master will defend
(4) The responsio, or body (corpus) of the article: the master's determination of the question
(5) Reply to each of the objections posed at the beginning.
Imagine a lecture hall (aula) filled with students--some sober, some not--on a feast day. The question is posed, and students begin to yell out objections from the audience (no microphones necessary). A scribe is writing down the objections, perhaps to be edited later in the case of less-than-sober objections. The master (or one of his faithful student-lackeys) comes up with a sed contra. At that point the master makes his determination and then replies to the objections.
The Summa Theologiae is not itself the record of such a scene (though several of St. Thomas's works--the so-called "Disputed Questions" (quaestiones disputatae) are indeed doctored records of such scenes), but St. Thomas nonetheless wrote the Summa Theologiae in the same style.