Because all knowledge and every definition is through the form, therefore, prime matter cannot be known or defined by itself, but by the composite: and so we say that prime matter is that which is related to all forms and all privations like the bronze is related to the statue and to the privation of some figure. And prime matter here means prime in an absolute way…

Notice carefully that some thing can be although it is not, whereas another thing truly is. That which can be is called being in potency; that which already is, is called being in act. But there are two kinds of being: namely essential being or the substantial being of the thing (as, for example, to be a man) and this is to be absolutely. The other kind of being is accidental being (as, for example, to be a white man), and this is to be after-a-fashion or in some qualified way.

Thomas Aquinas, OP ( 1225 – 7 March 1274), also Thomas of Aquin or Aquino, was an Italian Dominican friar and priest and an immensely influential philosopher and theologian in the tradition of scholasticism, within which he is also known as the "Doctor Angelicus", "Doctor Communis", and "Doctor Universalis". "Aquinas" is from the county of Aquino, an area his family held land in until 1137. He was born in Roccasecca, Italy.

He was the foremost classical proponent of natural theology, and the father of Thomism. His influence on Western thought is considerable, and much of modern philosophy was conceived in development or opposition of his ideas, particularly in the areas of ethics, natural law, metaphysics, and political theory. Unlike many currents in the Church of the time, Thomas embraced several ideas put forward by Aristotle — whom he referred to as "the Philosopher" — and attempted to synthethise Aristotelian philosophy with the principles of Christianity. The works for which he is best known are the Summa Theologica and the Summa contra Gentiles. His commentaries on Sacred Scripture and on Aristotle are an important part of his body of work. Furthermore, Thomas is distinguished for his eucharistic hymns, which form a part of the Church's liturgy.

Thomas is honored as a saint by the Catholic Church and is held to be the model teacher for those studying for the priesthood, and indeed the highest expression of both natural reason and speculative theology. In modern times, under papal directives, the study of his works was long used as a core of the required program of study for those seeking ordination as priests or deacons, as well as for those in religious formation and for other students of the sacred disciplines (Catholic philosophy, theology, history, liturgy, and canon law).

Also honored as a Doctor of the Church, Thomas is considered the Church's greatest theologian and philosopher. Pope Benedict XV declared: "This (Dominican) Order ... acquired new luster when the Church declared the teaching of Thomas to be her own and that Doctor, honored with the special praises of the Pontiffs, the master and patron of Catholic school