St. Thomas Aquinas’ Five Ways of Proving God’s Existence in Context
The most famous and widely read proofs for God’s existence are the Five Ways of St. Thomas Aquinas found at the beginning of his monumental magnum opus, the Summa Theologiae (or Summary of Theology). Despite their popularity and fame, they are often misunderstood, both by those advancing, as well as those opposing, their theistic conclusion. Much of the misunderstanding, however, arises when both the advocates and opponents fail to consider the historical and literary context of the proofs, and of their author.
Saint Thomas was born around 1225 to noble parents, being a younger son of the count of Aquino in central Italy. Despite being groomed for a career as a high-ranking churchman, when he was sent to study at the University of Naples he joined the young and unconventional Order of Preachers founded by St. Dominic, much to the consternation of his aristocratic family. After becoming a Dominican friar, Thomas was sent to the University of Paris to continue his studies. In these newly established universities at Naples and Paris, he was introduced to the natural science of the pre-Christian (pagan) philosopher, Aristotle. Aristotle lived around 350 BC, but his works on physics and biology were unknown in Christian Europe until about 100 years before the time of Aquinas. They had been preserved by scholars in the Middle East since around the time of the fall of the Western Roman Empire (AD 500), and then by Islamic philosophers and scientists, until they were introduced to Christian scholars in medieval Europe in the 12th century (in part as a result of the crusades). The writings of Aristotle and his Islamic commentators caused much turmoil in the Catholic universities since they at once offered powerful intellectual tools for understanding nature, yet seemed to challenge Catholic theology by teaching that the world was eternal (and so not created as the Bible teaches) and that there is a single collective mind for all people (and so each individual does not have an immortal soul). Many churchmen feared that reason and science (as represented by Aristotle and the Islamic philosophers) threatened the faith of Christians. Then, as now, some have indeed used them as weapons against the faith.
Thomas Aquinas stepped into this conflict and advanced a resolution which ultimately would allow science to flourish in Europe (when it had not been able to progress anywhere else). He championed the reliability of philosophy and science (referring to Aristotle as “the Philosopher”) and argued that reason, together with faith, can discover truth – a conflict between them being impossible since they both originate in God. As a Christian, he believed that God created both an orderly, intelligible, natural world and human reason which can understand it; he also believed that the same God is the principal author of the Sacred Scriptures, i.e., the Bible. Thomas claimed that the faith of Christians thus has nothing to fear from scientific investigations since the truths which God reveals through Scripture can never be contradicted by the truth of reason, so long as both faith and reason investigate their proper subject matter and are consistent with their own principles – that neither draws conclusions beyond the warrant of their own evidence. God reveals many truths about Himself in Scripture (though not a comprehensive knowledge of Himself), truths that could never be discovered by reason. But reason can know some truth about God apart from Scripture (at least for some few thinkers, after a long time and with the likely inclusion of many errors). This resolution granted to reason and science an autonomy and dignity which would allow for the independent investigation of nature within the Christian worldview.
Thomas wrote the Summa Theologiae as an introduction to theology for graduate students by presenting a comprehensive discussion of the philosophical and theological background necessary for higher studies. He offers proofs of God’s existence, not to convince those who otherwise did not believe God existed. In his time and place in Christian Europe, there just were no atheists to be convinced. Rather, he outlines these proofs as part of his discussion of how God, both His existence and nature, can be known by reason. Aquinas first shows how God’s existence can be known apart from faith and Scripture, yet is not so obvious as to be self-evident. Thus, he argues that God’s existence can, in principle, be proved from His effects, and then gives his Five Ways as examples of how reason does this by seeking to explain five kinds of effects, and the characteristic kinds of causality responsible for that effect.
These particular five proofs are based on different aspects of reality that Aquinas believes are apparent to an intelligent observer, aspects whose the ultimate explanation is God. They begin with the observation of motion, efficient causality, contingent beings, grades of perfection and goal seeking behavior. But more than simply considering these phenomena as effects, or things to be explained (explananda), each ‘way’ argues in terms of an intelligible character or ratio that is the proper to each proof. For he does not simply identify the ultimate cause of sensible material things; in a general sense, particular substances in the physical, sensible world are the common starting point for each distinct proof. Rather, he examines physical things (things in matter and motion) in terms of, or under the intelligibility of, different kinds of causality: the motion that causes them to move, the efficient causality that they manifest; their existence or being which, while underlying their motion and efficient causality, is also a distinct kind of intelligibility; their perfection in being, again which underlies their motion and efficient causality; and finally, their finality, or end-directedness, which is manifested in their motion, efficient causality, being, and perfection.
These particular five proofs are based on different aspects of reality that Aquinas believes are apparent to an intelligent observer, aspects whose the ultimate explanation is God. They begin with the observation of motion, efficient causality, contingent beings, grades of perfection and goal seeking behavior. But more than simply considering these phenomena as effects, or things to be explained (explananda), each ‘way’ argues in terms of an intelligible character or ratio that is the proper domain of each proof. In a general sense, particular substances in the physical, sensible world are the common starting point for each distinct proof. But Aquinas does not simply argue for an ultimate cause of all sensible material things taken as an undistinguished whole. Rather, he examines physical things (things in matter and motion) in terms of, or under the intelligibility of, different kinds of causality: the motion that causes them to move, the efficient causality that they manifest; their existence or being which, while underlying their motion and efficient causality, is also a distinct kind of intelligibility; their perfection in being, again which underlies their motion and efficient causality; and finally, their finality, or end-directedness, which is manifested in their motion, efficient causality, being, and perfection.
These are not the only proofs for God’s existence that Aquinas offers in his writings, so his choice of these five is based on his belief that they form the basis for inferring God’s basic attributes: immateriality, immutability and simplicity; omnipotence; necessity and eternity; goodness and perfection; and intelligence, wisdom and love. It is only after having derived these essentially divine attributes that Aquinas believes he has rationally established the existence and nature of what he recognizes as the God he believes in. Thus, while each proof ends with the phrase “and this everyone calls God” or its equivalent, Aquinas does not the identity of the First Cause of the proofs to have been established until he shows in the next twenty-four questions of the Summa Theologiae that the First Cause has these attributes.
By considering the historical and textual context of the Five Ways of St. Thomas Aquinas, one can more accurately understand and assess the value they have for demonstrating that God exists, as well as their role in the Summa Theologiae and in Aquinas’ work as a theologian and philosopher. This will, in turn, help one appreciate some of the tremendous impact Aquinas has had on the development of Western civilization.
Revised 5/24/2021
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