If you've looked at the excerpt from Aquinas' Summa Theologica, you will see that the articles are structure this way:
Enquiry Question: for example, "Can Angels think?"
Objections: (that is, arguments against Aquinas' thesis and the claims that why angels can't think);
Contrario ("On the contrary"): a simple statement of why the objections are wrong (Angels CAN think because of XYZ); and
Argument: a statement of Aquinas' thesis (detailed explanation of how we can know that angels think); followed finally by:
Responses: replies to the objections, and why they are wrong.
This is very standard format for Medieval academic writing. In fact, all Masters' students had to write defences, or summae, of their arguments like this.
The key thing to keep in mind is this: in the Middle Ages, scholars understood that there are several parts or levels to human reasoning:
Natural Reasoning (Cataphatic): things you can work out, just through experience and thinking about them;
Revealed Reasoning: things we could only know because God has revealed them to us (requiring FAITH);
Mystical Reasoning (Apophatic): things we know through personal, mystical experience. This kind of thinking is always balanced by the first and second kinds.
While today, most people think that belief in God is "Revealed" or "Faith", in the Middle Ages, they did not think so; they (and certainly Aquinas is making this argument), knowledge of the existence of God is natural reason, and does NOT require faith;
The fact, for example, that God is a Trinity (Father, Son, Holy Spirit) is NOT natural, and no one could know this just by thinking about it, and so this kind of knowledge IS faith-based, or revealed.
We see this kind of understanding of reasoning throughout medieval literature, even in "bawdy" or crude writing, such as the poem of Gwerful Mechain. Can you see it?