Matter and form are two notions lying at the very heart of Aquinas’s broadly Aristotelian conception of reality. Aquinas inherits these notions from Aristotle (hyle and morphe in Greek), and his understanding of each is shaped to a large extent by the various uses to which Aristotle himself puts them. Even so, the precise nature of Aquinas’s hylomorphism, as well as its centrality in his thought, are of independent significance. Indeed, it would be impossible to understand Aquinas’s fundamental divisions of reality – including the division of God and creature, substance and accident, body and spirit – apart from his own particular conception of matter and form. It would also be impossible, apart from this same conception, to appreciate the elements of an explanatory framework that Aquinas deploys in almost all his writings – including potentiality and actuality, principles and causes, and the fourfold division of causes into material, formal, efficient, and final. In short, to acquire a familiarity with the details of Aquinas’s understanding of matter and form is almost to become accustomed to his distinctive vision of reality.

There is a real question about whether Anselm developed anything like a systematic ethical theory. Indeed, scholars have sometimes suggested that his treatment of ethical matters consists in little more than recapitulation of ethical principles implicit in Scripture or transmitted to him by Christian thinkers such as Augustine and Boethius. The truth of the matter, however, is quite the opposite. Although it is easy to overlook the systematic nature of Anselm's ethical theorizing, as well as its genuine originality, his contribution to medieval ethical theory is considerable. Admittedly, none of his philosophical or theological works is devoted to the systematic presentation of ethical issues; nor is there much novelty to be found in them at the level of specific ethical principles. Nonetheless, it is possible to extract from his works something that moral philosophers today would recognize as a worked-out ethical theory - one that includes a sophisticated moral metaphysics, moral semantics, and moral psychology.

Peter Abelard (1079-1142) is a philosopher and theologian whose reputation has always preceded him. Indeed, to this day he remains among the best-known figures of the entire Middle Ages. Although one can hardly overestimate the value of his intellectual legacy, his reputation owes at least as much to his flamboyant personality and to the sensational details of his biography. Very early on Abelard established his place as one of the most celebrated masters in Paris by challenging - and then defeating - his teachers and rivals in public disputation. In some cases, he literally drove these rivals out of business: he stole their students and set up his own schools (the first when he was only twenty-five) just down the road from them. He aroused the fiercest devotion in students, and the fiercest enmity in rivals. He also inspired the love and devotion of (some would say merely seduced) a seventeen-year-old Heloise. But when Heloise became pregnant and ran away with him to be secretly married, Abelard earned the hatred of her uncle and guardian, Fulbert, who was also the canon of Notre Dame.

During the Middle Ages, theology is the preeminent academic discipline and, as a result, most great thinkers of this period are highly trained theologians. Although this much is common knowledge, it is sometimes overlooked that the systematic nature of medieval theology led its practitioners to develop full treatments of virtually every area within philosophy. Indeed, theological reflection not only provides the main context in which the medievals theorize about what we would now recognize as distinctively philosophical issues, but it is responsible for some of their most significant philosophical contributions. To give just a few examples: it is problems with the Christian doctrine of the Incarnation that prompt medievals to develop the notions of substance and person in striking and original ways; it is problems with the doctrine of the Eucharist that lead them to consider the possibility of accidents that do not inhere; and it is problems of interpreting particular scriptural texts, such as the Book of Job, that introduce refinements in their understanding of the nature and purpose of evil.