 Some time after 1248, he set aside the common scholastic ways of teaching in order to devote time to languages and experimental concerns. Thus, we can see the period from c. 1240–48 as the time during which he lectured at Paris on Aristotle, on Grammar/Logic, and especially on the mathematical subjects of the Quadrivium. And so, depending on the chosen year of birth, the chronology would be as follows: (1) Bacon was born c. 1214, educated at Oxford c. 1228–36, Master of Arts at Paris c. 1237–47/8, Private Scholar 1248–56/7, active again at Oxford c. 1248–51, back in Paris 1251, Franciscan Friar at Paris c. 1256–57 to 1279, returning to Oxford c. 1280, died c. 1292. Or: (2) Bacon was born c. 1220, educated at Oxford c. 1234–42; Master of Arts at Paris c. 1242–47/8, active again at Oxford c. 1248–51, back in Paris 1251, Franciscan Friar at Paris 1256/7 to 1279, returning to Oxford c. 1280, died c. 1292. Further precision on the chronology must await the critical edition of all the works of Roger Bacon and careful scientific study of these works in relation to other thirteenth century scholars.