The great medieval Christian thinkers would have been bewildered by today's idea that faith and reason are fundamentally at odds. Although their outlooks varied widely, they agreed that philosophical reasoning could and should be used to defend and elucidate the doctrines of the Christian faith.
Augustine found Platonism compelling and adopted much of it, while seeing that Christian belief required him to modify it in several ways. The doctrine of the Incarnation in particular challenges Platonism's negative view of the body and the material world, in contrast with the perfect realm of the mind.
Augustine argued that the search for truth must begin with the acceptance of authority. Historical claims must be accepted or rejected on the basis of authoritative testimony. Christianity involves such historical claims, and Augustine sought to show that it is reasonable to accept the testimony on which Christianity rests.
According to Augustine, because God is good, everything he creates is good; and because God is creator, nothing exists that he does not create. The origin of evil is therefore perplexing. Part of Augustine's solution was to argue that evil, in itself, is not anything. It is a mere privation: a lack of measure, form, or order.
Awaiting execution, Boethius wrote one of the most beloved books of the Middle Ages, The Consolation of Philosophy. Why does he seek comfort in philosophy and not in scripture? His inability to see the universe as a rationally coherent system called for the therapy of reason, as manifested in philosophy.
The Consolation of Philosophydiscusses the problem of divine foreknowledge and human freedom. If God's foreknowledge is infallible, our actions are necessary. Boethius used the doctrine of divine eternity to show how our actions are not necessary in any sense that threatens freedom or moral responsibility.
Anselm helped revive the technique of philosophical argument known as dialectic, applying it systematically to theological discussions. The doctrines of the Christian faith are, to Anselm, intrinsically rational because they concern the nature and activity of God, who is himself supreme reason.
Anselm asserted that we can prove God's existence and attributes by exploring the idea of God as "that than which a greater cannot be thought." A monk named Gaunilo countered that Anselm's argument—now known as the "ontological argument"—also proved the existence of the greatest conceivable island, which is nonsense.
The ontological argument establishes so many different divine attributes that it is difficult to see how one and the same being can possess all of them at once. Anselm resolved this problem by using dialectic to analyze each case, such as the apparent conflict between God's mercy and his justice.
If everything we have is received from God, then God deserves all the praise for our good works and all the blame for our evil deeds. In a move typical of medieval philosophers, Anselm simplifies this problem by looking at the case of angels. God gave all the angels the will to persevere in justice, but the evil angels abandoned that will.
Famously scandalous in his personal life, Abelard courted controversy in philosophy and theology as well. He gave a brilliant analysis of the Trinity in three treatises: the first was condemned and burned; the second was left unfinished; the third was also condemned, ending Abelard's teaching career.
o Abelard, the death of Christ delivers us from the punishment for the sin of our first parents, thereby inspiring our gratitude and enabling us to serve God out of love rather than out of fear.
The recovery of most of Aristotle's works by the middle of the 13th century coincided with the rise of the universities. Aristotle's thought was attractive because it was wide-ranging, systematic, and rigorously argued; it seemed dangerous because many of its teachings contradicted Christian doctrine.
Bonaventure's account of the mind's journey to God takes a critical approach to Aristotle. In his account of creation, Bonaventure rejects the Aristotelian doctrine that the world has always existed; but in his account of theoretical knowledge, he tries to synthesize the Aristotelian and Augustinian views.
Regarded as one of the three luminaries of medieval philosophy's golden age (together with Scotus and Ockham), Aquinas followed Aristotle in contending that all knowledge derives from sense experience. Thus humans can know only those facts about God that are evident from reflection upon sense experience.
In his five proofs for the existence of God, Aquinas first answers objections that the existence of God cannot be proved, using the scholastic method to examine the two sides of the question. Then he proceeds to the five proofs, the first of which argues that there must be an initial, unmoved mover: God.
How can the words we use for ordinary objects be meaningful when applied to God? Aquinas answered that created things resemble their Creator; we can therefore use the language of ordinary experience to speak meaningfully about God, although our words cannot have exactly the same meanings in both spheres.
Aristotle's view that the soul is the form of the body implies that when a human organism ceases to live, the soul ceases to exist. But Aquinas argued that we can prove philosophically that the soul survives bodily death. The resurrection of the body, however, is a mystery of faith that cannot be proved by reason.
For Aquinas, natural happiness sets the standards of natural law, and natural virtues dispose us to attain such happiness. But in addition there must be supernatural virtues that dispose us to attain supernatural happiness. Natural virtues are attained by moral development; supernatural virtues are acquired by divine gift.
Even during his life, the adjective "subtle" had come to be associated with Scotus's thought, which is ingenious, difficult, and inventively defended. As a Franciscan, he regarded the will as a power higher than the intellect, and he followed this emphasis in his account of both divine and human freedom.
Scotus went much further than Aquinas in rejecting the approach to discourse about God that emphasizes what God is not. Scotus argued that it is possible by natural means (i.e., without supernatural help) for the human intellect in this present life to acquire a concept in which God, and God alone, is grasped.
Ockham employed the principle that has come to be called "Ockham's razor" in reducing the basic categories in the Aristotelian inventory. He also argued against the reality of universals—entities like "whiteness" that exist beyond the whiteness of a particular piece of paper, snowdrift, and so on.
Ockham rejected the idea that Christian theology is an intellectual enterprise that aspires to the same standards as pagan philosophy. Although he agreed with Aquinas and Scotus that reason needs to be supplemented and repaired by faith, he was deeply skeptical about the prospects for proving that God exists or showing that the mysteries of faith are consonant with reason.
By the 14th century the loss of confidence in Aristotelian philosophy had led some philosophers to conclude that the domain of Christian faith and the domain of philosophical reasoning have no overlap. With the dawn of the Renaissance, Aristotelianism was rapidly losing ground to a new, more mystical version of Platonism.