Thomas Aquinas (1225–1274) was a primary Catholic thinker who sought to Christianize Aristotle just as Augustine adapted Neoplatonism. He also, to the satisfaction of many, reconciled the dilemma of Faith versus Reason.
Augustinian thinking was the accepted school of the day, and it did not see any distinction between philosophy and theology, yet steadfastly stuck to the theory of illumination. In other words, divine intervention was necessary for profound intellectual advancements.
Thomas Aquinas rejected both illumination and the Double Truth. In regard to Averroism, he believed that religion and reason did not each represent a separate truth. There cannot be two opposing and competing truths — there is one Truth. Philosophy and theology are not in opposition; they are on parallel courses. Some things are self-evident, and others require a leap of faith.
The Averroist theory of the Double Truth stated that philosophy and theology were mutually exclusive. There is truth that comes from philosophy, and the truth that comes from theology, but they are parallel truths.
Thomas Aquinas gave more credit to the human intellect than Augustine did. Mankind did not need divine intervention to think profound thoughts. One can ascertain the Form by observation of the reality. We can conceive of the exalted notions of Truth and Beauty without a celestial nudge. In fact, mankind cannot truly grasp the Forms, because like Aristotle, Thomas Aquinas felt the Form was embedded in the corporeal reality and was not a free-floating entity out there in the ether. Harkening back to Aristotle, and with a little Christian pride, Thomas Aquinas believed that if a “pagan” like Aristotle can figure all this out, Christians certainly could. Old Aristotle did not have the advantage of divine assistance, pagan that he was.
Another welcome contribution of Thomas Aquinas was his holistic approach to the body-mind-spirit that makes a human being. There was less of “the spirit is willing, but the flesh is weak” thinking in his philosophy than in Augustine's and Plato's.
Thomas Aquinas also postulated five ways that we can prove the existence of God:
Motion is a reality, at least to human perception. For every motion, there is a prior impetus that set it in motion. Go back far enough, and you have the Primary Mover. This is God.
Similarly, new things come into being all the time. For each of these events, there must be a cause. Regress cause after cause until you get to the first. There you will find God.
All things change, and all things are contingent upon something else for their existence. Ultimately there will be something original that is not contingent on anything else for its existence. Therein lies God.
Thomas Aquinas suggests that you take a look around you and note that there is an inherent perfection to the nature of things, to greater and lesser degrees. There must be something that is purely perfect, from which all other things descend in a perfection pecking order. Mr. Perfect himself is God.
Order exists everywhere. There is a profound order to the universe. Ergo, there must exist an intelligence responsible for this magnificent orderliness. This is God.
Motion, cause, contingency, perfection, and order are Thomas Aquinas's five proofs for the existence of God. Many have disagreed with it, but it was a big hit in its day.
Thomas Aquinas did for Aristotle what Augustine did for Plato, making the “pagan” philosopher appear to seamlessly blend right in with the teachings of the Christian Church. Aquinas is regarded by many as the man who successfully ended the discrepancy between faith and reason.
In addition to the dilemma of Faith versus Reason, the other problem in medieval philosophy was the problem of the Universals. Universals are Aristotle's attempt to make sense of the Platonic Forms. Plato believed that Forms were divine entities (called Truth, Beauty, and so on) that are floating around out there in the ether, and that earthly notions of truth and beauty are mere shadows of the forms. Aristotle felt that there were Universals within substantial objects, and that these Universals were not separate entities.
Because much of the classical writings of Plato and Aristotle were lost during the Dark and Middle Ages, to be rediscovered later during the Renaissance, the medieval philosophers were debating this notion all over again. Aquinas comes to the same conclusion as Aristotle, some 900 years later.
Aquinas also concurs with the Aristotelian view that physical reality is simultaneously composed of both its actuality (what it is) and potentiality (what it will become). This is an Aristotelian/Aquinian principle. Also, physical reality is composed of both matter and form — Aristotle's Universals theory.
Aquinas divided knowledge into two stages, sensitive and intelligent.
Sensitive knowledge is simple awareness of something, such as a rock.
Intelligence is grasping the abstract concept of “rock.” He divided intelligence into three processes: abstraction, judgment, and reasoning.
Though Aquinas died young (he was only fifty), his legacy in both philosophy and theology is significant. His body of work is enormous, as was his physical girth. Rewarded posthumously with sainthood by the Catholic Church, even secular humanists continue to marvel at his keen intellect and contribution to philosophy.