The Five Ways are a set of five logical arguments written and crafted by St. Thomas Aquinas in the 13th century. The Five Ways were originally part of Aquinas’ Summa Theologica, a massive instructional guide for theology students that houses many of the main teachings of the Catholic faith today. Unlike the ontological arguments, Aquinas’ Five Ways are a posteriori in nature. Thus, the very foundations of the Five Ways are based in experience and empirical evidence. Should his arguments prove valid, the existence of God would be a proven fact on par with the many discoveries of modern science. Likewise, because the Five Ways are partially based on sensory observation of the real world, they will never be able to establish the existence of God with complete certainty due to the infallibility of sensory experience.
While the Five Ways as whole can be characterized as being cosmological arguments, the first three in particular are especially representative of the cosmologic arguments while the last has been described as teleological in nature.
Even though it may not be apparent at first glance, the Five Ways are heavily influenced by Aristotle’s physics and metaphysics. Consequently, knowledge in Aristolean physics is necessary in order to fully understand the complexity of Aquinas’ arguments. It might be beneficial to first skim through the main outline of all five ways before studying the influence of Aristotle on Aquinas’ arguments.
The Aristotelean Background
While Aquinas’ arguments can be understood without knowledge of Aristotelian physics, having this background will be vital to fully understanding Aquinas’ argument given that Aristotle’s philosophy had a tremendous influence on them. However, this isn’t to say that Aristotle is the sole philosopher to have influenced Aquinas; historians believe that many others also impacted Aquinas and the formulation of his arguments in more subtle ways.
Platonic Forms
Before we begin our discussion on Plato’s Theory of Platonic Forms, a disclaimer is in order. First off, Aristotle was not a Platonist and rejected the Platonic Forms all together. Similarly, neither was Aquinas, although the theory of Platonic Forms seems to have some influence on Aquinas’ fourth way. The connection between the two will be laid in more detail in later sections.
To Plato, the Platonic Forms are perfect representations of what each individual thing is supposed to be like in order for it to be that specific thing. Every idea in the physical world as we know it, therefore, is based off its Form; the Form of an object depicts the qualities needed in order to be considered that object. For example, we can draw a number of different triangles in a number of different ways. We can do so on paper using a pen, or we can have a computer generate one for us. However, regardless of how we do it, it’ll never be a perfect representation of the Form triangle. Likewise, the Form triangle lists out the necessary qualities needed in order for something to be considered a triangle.
Even though it doesn’t appear as though Forms exist in reality, Plato contested that the Forms are transcendent to our own world and instead are essentially the basis of our own reality. In other words, according to Plato, the Forms exist in the real, abstract world while our own physical world is a shadow/approximation of that real world.
Taken all together, no object is a perfect representation of the idea it’s intended to represent. Every object in the physical world is simply a flawed version of its perfect Form. Consequently, the Forms can be thought of as a family of the purest and most real things in existence.
Even though the Theory of Forms influenced Aquinas’ thinking in the fourth way, Aquinas never considered God to be a Platonic Form. Instead, what’s important is the distinction between flawed, corporeal beings (humans) and a perfect, incorporeal being (God).
Aristotle's Four Causes
From Aristotle’s perspective, we never truly have knowledge of a particular thing unless we can understand its cause, or rather, its why. He thus argued that all objects have four different causes: the material cause, the formal cause, the efficient cause, and the final cause.
Material Cause - All objects and things in existence are made of some sort of material or substance. When we refer to what something is comprised of, we’re referring to it’s material cause.
Formal Cause - Likewise, all objects and things in existence have a shape, form, appearance, etc. When we refer to an object’s shape and form, we’re referring to it’s formal cause.
Efficient Cause - Everything that currently exists must’ve been caused by something else. A table must’ve been made by someone, and a tree must’ve grown from a seed from a different tree. All things, therefore, have an efficient cause, or the cause of its existence.
Final Cause - Lastly, Aristotle noted that all things in the world serve a purpose or have an end that they will eventually obtain. The purpose of a table is to support objects that are placed upon it; the purpose of an acorn is to develop into a tree; the purpose of sailboat is to sail. An object’s purpose or end is it’s final cause.
Only two of Aquinas’ arguments are based in Aristotle’s Four Causes; the second way is based on the notion of efficient causes while the fifth involves the concept of final cause.
Law of Non-contradiction
While the Law of Non-contradiction has been thoroughly discussed by many in the ancient world, the traditional source of the law originates from Aristotle’s Metaphysics. The Law of Non-contradiction is the principle that it is impossible for a thing to be and not be at the same time in the same manner. A rabbit cannot be both dead and alive at the same time, and a glass of water cannot be simultaneously full and empty. In other words, A is not not-A, and not-A is not A. The significance of the Law of Non-contradiction is apparent when applied in tandem with the metaphysics of potency and act.
Metaphysics of Potency and Act
How, then, are we to understand the concept of change under the Law of Non-contradiction? Let us argue, for a moment, that a thing cannot change itself. If a thing cannot change itself, something else must change it. If we follow this line of logic, we must conclude that being cannot change itself, and when we refer to being, we refer to all things in existence. Therefore, being must be changed by non-being. But non-being doesn’t exist. How are we to solve this dilemma of change? Aristotle provided a solution to the argument above by stating that two different manifestations of being existed—potentiality and actuality.
Potentiality, or potency, is essentially an intermediary state between being and non-being. It’s the potential to receive a different form, the capacity the become a defined existing thing. Actuality, on the other hand, is a fully developed state of being.
Imagine a tall brick of marble untouched by a sculptor. Before the sculptor begins his work, the marble has the potency to become a statute. Once the sculptor finishes sculpting the marble, potency becomes actuality, and the marble brick becomes a statute. The same thought process can be applied for other instances in nature. A puppy is in potency to become a dog. A seed is in potency to becoming a plant. Milk is in potency to becoming expired milk.
If we combine the metaphysics of potency and act with the law of non-contradiction, we must conclude that it is impossible for something to be in potency and actuality at the same time. A puppy may have the potency to becoming a full-grown dog, but it cannot somehow be both.
Aquinas’ subsequent arguments rely heavily on the law of non-contradiction and the metaphysics of potency and actuality to explain the causal beginnings of nature. By utilizing these ideas, his cosmological proofs seek to demonstrate that God is the logical beginning of many aspects of the natural world.