One of the principal methods of Scholasticism was the use of the logic and philosophic vocabulary of Aristotle in teaching, demonstration, and discussion. Another important method was the practice of teaching a text by means of a commentary by some accepted authority. In philosophy, this authority was usually Aristotle. In theology, the principal texts were the Bible and the Sententiarum Libri Quatuor (Four Books of Sentences) by the 12th-century Italian theologian and prelate Peter Lombard, a collection of the opinions of the early Fathers of the Church on problems of theology. The early Scholastics began by adhering closely to the text on which they were commenting. Gradually, as the practice of critical reading developed their own powers of thinking, they began to introduce many supplementary commentaries on points, known as disputed questions, which either were not covered or were not adequately solved by the text itself.