Thomas Aquinas is often called the greatest philosopher and theologian of the late middle ages. While Augustine baptized Plato and wedded what is valuable in Platonism to Christianity, Aquinas can be thought to have done the same thing with Aristotle. Stylistically, this shows itself by Aquinas's use of the term "the Philosopher"-for Aquinas the philosopher is Aristotle. Aquinas's adaptations of Aristotle were considered bold and modern in the thirteenth century. Aristotelianism was gaining wide influence as the best scientific understanding then available of the world, but it seemed to many to be incompatible with Christianity. Aquinas was convinced that the on-going intellectual health of Christianity required engagement with the cutting edge of intellectual inquiry. (In this, he was indebted to Augustine.) Moreover, he was convinced that many truths about reality are available through the correct exercise of natural human reason. For Aquinas, Aristotle's philosophy contained much that was correct.

Aquinas did not, however, follow Aristotle slavishly. Aquinas thought that crucial parts of reality transcend natural human reason. Humans can only know these things through the revelation of God's divine acts in history, as recounted in scripture, most crucially the incarnation, life, death, resurrection, and ascension of Jesus Christ, and through the work of the Holy Spirit in the Church. God's revelation, thus conceived, was historically inaccessible to Aristotle, but Aquinas so admired Aristotle's philosophical position (achieved through natural reason alone) that he believed it, too, to be a gift of God.

The distinction between natural reason and revelation is the foundation for the distinction between philosophy and theology. Philosophy can discover truths and make deductions about human nature as it relates to this world. It gives a true, but partial, view of human nature. Theology can go beyond philosophy and draw conclusions about reality and human nature based on revelation and faith. God has revealed that human beings fully flourish only in relation to an eternal, intimate relationship with God through Jesus Christ. This supernatural calling outstrips natural human capacities and is a gift of grace infused into human nature by God.

Although philosophy and theology are distinct for Aquinas, they are not disjoint. Some truths are a part of both subjects. According to Aquinas, this is true of the existence of God. Aquinas thinks that unaided human reason can be employed to demonstrate the existence of God. He does this, famously, in his Five Ways. Several of these arguments owe a large debt to Aristotle. While unaided reason can prove God's existence, God has also chosen to reveal this truth in other ways. Many people, believe in God's existence by faith, without benefit of philosophy. These people may not know that there are sound arguments for the existence of God or may not have the philosophical skill to understand and grasp their correctness. While Aquinas thinks that reason could show God's existence, he also thinks that many truths about God (e.g. that God is triune, that God was incarnate in Jesus Christ) transcend reason and can only be known through faith. These truths and the deductions that can be made from them constitute parts of theology which are outside philosophy.

Aquinas's account of the virtues carries through this distinction. Aquinas thinks that some virtues are aimed at the limited human happiness achievable in this life through our natural capacities. He calls these "natural virtues" and follows Aristotle and Plato in his account of them. He recognizes the same four cardinal virtues that Plato discusses in the Republic and also agrees with Aristotle's doctrine of the mean. However, Aquinas thinks that to understand human nature fully, we must consider redeemed human nature. Redemption equips us for union with God by infusing us with the theological virtues of faith, hope, and love, mentioned by Paul in I Corinthians 13. These virtues do not just rest on top of our natural virtues like frosting on a cake, but permeate and elevate all our natural virtues. For example, the natural virtue of courage, which would allow us to have the mean of fear when faced with danger, becomes the ability to face martyrdom for the cause of Christ if necessary.

Aquinas shows the complex dialogue between philosophy and theology in his style. He uses a question/answer format, but his answer is always embedded in a web of dialogue with alternative views. After stating his question, Aquinas always first considers the reasons for the view he will ultimately reject. He then says "On the contrary:" and states the opposite view, which is usually closer to his own view. After explaining his view more fully under the label "Response," he then gives replies which show why the reasons given for the view he rejects are inadequate. Some readers find that it is less confusing to go to the center section under each question first so that they can focus more easily of Aquinas view. After reading it and seeing "where he is coming from," they can then explore his evaluation of alternatives.

Aquinas's style is a product of the debate format common in his day. Once one is used to it, this format can build drama and suspense. Sometimes the objections that Aquinas lists before coming to his own view seem very persuasive. How will he answer? How will he get himself out of this one? The format also embodies an attractive intellectual hospitality. He is willing to "hear out" those who disagree with him before he speaks. In a sense he is graciously yielding something to them that is his by rights: home court advantage. Thus, even Aquinas's style embodies important Christian virtues.

Aquinas says, "We must love them both, those whose opinions we share and those whose opinions we reject. For both have labored in the search for truth and both have helped us in the finding of it." Whether or not you end up agreeing with Aquinas's views, his synthesis of Christianity and Aristotelian philosophy is an impressive intellectual achievement. It raises vital questions about the good life: Does God exist? What is the nature of faith? Is there a life that transcends this world? Can we be virtuous without grace? What is the relationship between being a good person and being a good Christian?