The main philosophers of the Middle Ages were religious thinkers; St Augustine (354- 430 CE) and Thomas Aquinas (1225-1274 CE) for Christianity and Averroes ( 1126-1198 CE) for Islam.
Augustine was influenced by the thinking of Plato and the teachings of the Neo-Platonist, Plotinus (204–270 CE). He thought that faith and reason could be reconciled within Christianity. Augustine adopted Neo-Platonic thought on the immortality of the human soul, the notion of a world beyond the senses as well as Plato’s ideal forms, with the form of the good sitting above all reality. Through Augustine these ideas became a part of the Christian tradition.
Augustine’s main preoccupation was reconciling the existence of evil with the notion of a God that was all powerful and all merciful. He claimed to have resolved this apparent contradiction through his idea that God had given human beings free will so that they could choose between good and evil. Thus human beings bring evil on ourselves because we actively choose corruptible elements of the physical world rather than the eternal, perfect forms, which are spiritual.
Despite his views on free will, Augustine believed that God had already pre-determined (before people are born) those who will be saved and go to heaven. He also believed that due to Adam and Eve’s disobedience of God in the Garden of Eden, all human beings are born as wrong-doers or sinners. This is the notion of “original sin”.
Thus Augustine’s views seems to lack coherence. It is difficult to comprehend the purpose of “free will” if all human beings are “born bad” and if God has already determined who will be saved before a person even has a chance to exercise free will by choosing between good and evil. Perhaps Augustine’s philosophy has no real point apart from the attempt to reconcile the notion of a God who is supposed to be all powerful and all merciful with the obvious existence of evil.
Augustine’s other important view, in a historical sense, was that the relationship between human beings and God must be managed through the Catholic Church. This view dominated religion, and indeed the whole structure of society, throughout the Middle Ages. It lasted until Luther and the advent of Protestantism which taught that individuals could form their own direct relationships with God.
During the Middle Ages, the Islamic world was responsible for keeping alive Greek thought, especially the works of Aristotle. In Islamic Spain Averroes made extensive commentaries on Aristotle’s work which were a foundation for the Aristotelian revival in the 12th and 13th centuries.
Averroes supported Aristotle’s empiricism against Neo-Platonism and argued there was no incompatibility between Aristotle’s philosophy and religion. Wherever the Qur’an was not compatible with a rational approach Averroes held that it should be understood in a non-literal, metaphorical manner. But he also believed that only educated scholars would be able to understand the poetic metaphors and that common people should therefore remain content with a literal interpretation of the Qur’an lest they become confused. Ironically this mirrored Plato’s view of the common people being like prisoners in a cave., unable to ever comprehend the “true” nature of reality.
Before Thomas Aquinas, Aristotle’s empiricist approach had not been integrated into Christianity- it was seen as too ‘earthly’. Plato’s ideas of a perfect world of ideal forms existing independent of human beings and sitting above the sensual world of experience fitted better with Christian mysticism. Really all that was necessary was to substitute “God” for the form of the good- the supreme form according to Plato. Aquinas however drew upon both Plato and Aristotle and held both could be compatible with Christianity.
From Plato he derived the notion of the “essence of things”. Thus we can conceive of the essence of a dragon but still deny its existence. He argued that as God designed everything the essence of a thing must precede its existence. But he also took from Aristotle the idea that we acquire knowledge through the senses.
Aquinas developed his five “proofs” for the existence of God from Aristotle’s notion of causes. He argued, for example that the universe has a plan (Aristotle’s formal cause) must have a maker or first cause, being God (Aristotle’s efficient cause) and that everything in the universe works to a purpose, namely God (Aristotle’s final cause).
Aquinas also interpreted Aristotle as supporting the existence of “natural law”. Aquinas conceived of natural law existing in a separate realm to human law. Natural law was seen as reflecting the purposes that God must have built into things.
Thus Aquinas holds that “Whatever is a means of preserving human life and of warding off its obstacles belongs to natural law”.
Some claim that the concept of natural law underlies modern concepts of human rights. The idea here is that if there is a natural law which is fundamental to being human, then there must be natural rights. But neither Aquinas or other philosophers of his time ever referred to “human rights”.
More certainly it is the notion of natural law that lies behind Catholic doctrinal teaching against homosexual acts, masturbation and oral sex. All of these are seen as use of genitalia contrary to the “natural purpose” for which God created them, namely procreation.
Natural law has also been referred as a basis for “just war” theory.