In 1248 went to Cologne in order to found a Studium Generale and took Thomas with him who until 1252 acted as his assistant and was also charged with an important teaching experience. It is likely that at Cologne Thomas was ordained to the priesthood while it is certain that he frequented Master Albert's lectures on the De divinis nominibus of Pseudo-Dionysius and the Nicomachean ethics of Aristotle.

Thomas quickly demonstrated his speculative powers, but he also came to be called affectionately the dumb ox of Sicily perhaps because of his reserve. The comment by Master Albert was that soon the dumb ox with the bellowing of his doctrine will be heard to the ends of the earth. As a lector in theology and a bachelor in Biblical studies, Thomas gave an initial, cursory reading of the text, that is to say a brief commentary and summary but not an analysis. The aim was a literal comprehension of the sacred text. It is in this period, as bachelor of Biblical studies, that Thomas's first theological work, his Expositio super Isaiam ad litteram, belongs.