In the mid-13th century when Aquinas was working, new texts particularly texts of Aristotle were being reincorporated and rediscovered in the Western tradition, with Aristotle being the most important philosophical figure for Aquinas's intellectual project.

While Aquinas is profoundly learned and knows the entire accessible classical tradition of the mid-13th century (including most of Plato, Cicero, and other classical philosophers), most of Plato was unavailable to him, but he had access to texts like Cicero which were very important for his understanding of natural law and classical tradition elements.

Aquinas borrows from Aristotle a tendency toward system-building and encyclopedism, evident in his great works (Summa Theologiae, Summa Contra Gentiles) which constitute vast intellectual edifices spanning volumes covering every conceivable problem in morals, politics, theology, physics, and ethics with encyclopedic scope.

Prior to Aquinas, Christianity since the time of Augustine had been saturated in the Platonic tradition, with Plato being the most important and influential philosopher for Saint Augustine, and the primary influence on the connection between Christianity and Greece from Augustine through around 1100-1200 came from the limited number of available Platonic works.

Aquinas brings together all parts of two separate intellectual traditions—classical Greek-Roman philosophy and Christian theology—finding a harmonious and felicitous way of braiding these traditions together, though the fundamental difficulty lies in trying to square the circle because faith and reason ultimately don't mesh very nicely.

Aquinas shifts away from the Augustinian and Platonic tradition into an Aristotelian tradition characterized by: (1) greater concern with concrete things rather than abstract forms, and (2) use of syllogistic logic as the medium through which scholastic thinkers make arguments and articulate views, following Aristotle as one of the greatest logicians who developed the theory of the syllogism.

The speaker confesses to a suspicion that when reading Aquinas something is being overlooked and the synthesis works a little too well, suggesting possible unintentional or tendentious misreading in the attempt to make faith and reason cohere perfectly.

Aquinas successfully 'pulls the fangs of the monster' by making Aristotelian learning appear to be intellectually friendly or at least somewhat consistent with Christianity through sometimes ingenious and sometimes disingenuous readings of Aristotle, thereby preventing a sharp discontinuity and creating a merging of intellectual traditions that looks easy and effortless but is exceedingly difficult to accomplish.

The connection of sacred and secular that is found in the Middle Ages is characteristic of most highly developed pre-industrial cultures, and there are many interesting and rewarding comparative historical observations to be made from studying this phenomenon.

Nominalism is the doctrine that general terms like 'dog' are not references to transcendent forms but rather are names or shorthand for contingent sets of things with shared attributes (four legs, eating meat, responding to calls), representing a characteristically empiricist and Wittgensteinian approach to language.

Thomas Aquinas was the greatest figure in the development of medieval philosophy of Christianity called scholasticism, and his philosophy (Thomism) successfully synthesized Greco-Roman and Christian traditions by incorporating classical pagan learning into Christian theology established after the fall of the Roman Empire.

Aquinas borrows from the Platonic tradition the question-and-answer format used in Plato's dialogues, but in a frozen, petrified, and fossilized form: rather than living human beings engaging in open-ended playful pursuit of truth, Aquinas presents disembodied questioning followed by a series of answers concluding in an unplatonic or unsocratic final answer that represents the real truth.

Albert the Great gave Aquinas access to Aristotle and a wide body of Christian learning, and was particularly interested in Islamic and Jewish learning, especially Islamic and Jewish Aristotelianism, making Aquinas familiar with thinkers like Maimonides and his Guide for the Perplexed.

The reintroduction of classical learning into Western Europe from the 13th century onward should be understood as a process rather than an event, and one of the things that makes this process seamless and smooth during the Middle Ages is the great genius of Thomas Aquinas in synthesizing diverse intellectual traditions.

The problem of universals (how general terms like 'dog' or 'paper' apply to multiple individual instances) has been debated within scholastic logic and Platonic idealism, with medieval philosophers adopting either realism (that universals really exist as forms outside space and time) or nominalism (that universals are just names for sets of things with shared properties).

Aquinas's first way of demonstrating God's existence is the prime mover argument: observing that things move and things only move when something moves them, he infers that there must be a first mover that causes the initial motion in a chain of causes—an unmoved mover that does not itself move but is what everybody means by God.

Aquinas's third way is the argument from contingency: observing that all things in the physical world are contingent (they come into being and pass out of being), he infers by the principle of non-vacuous contrast that if contingent beings exist, there must be a necessary being that does not depend on anything else—which is what all agree is God.

Aquinas's fourth way is the argument from degrees of perfection: observing that things have different degrees of goodness and perfection (some math is better than others, some pie is better than others), he infers that this gradation toward a limit implies a final perfection or maximum goodness that must be God.

Connected with Aquinas's thinking in the Summa is an ontological doctrine called the Great Chain of Being, which holds that God has constructed the world in a perfectly and completely hierarchical way, with God at the top, then angels, then humans (with gradations among humans), then animals and plants, each level having a specific place ordained by divine will.

In the Great Chain of Being, the king occupies a position at the top of human hierarchy and rules by the grace of God and divine ordination, with legitimacy depending on consistency with natural law and divine ordinance, a framework that leads to the divine right of kings and a defense of Catholic absolutism.