St. Thomas Aquinas (1224-1274) was a Dominican priest, theologian, and philosopher. In one of his most famous works, the Summa, Theologiae, Aquinas put forward five proofs for the existence of God. Three of his ways, which will be discussed in this essay start with the observation of motion, efficient causation and contingency. The other two are the argument for Degrees and Perfection and The Argument from Intelligent Design. This is a posterior argument meaning a truth is learnt following an experience. This is contrasted with a priori, which means truths are not learnt on the basis of experience, instead the truth is known prior to the experience. For example 2+2=4. In simplest form, the argument states that the world exists and we know this because of observation (A). The existence of this world has a cause (A-B). The cause of the world is God – an identity claim. (B=C).
St. Thomas Aquinas, who was studying Aristotle, a Greek philosopher, concluded from common observations that objects can move or can be in motion. This motion can take three forms: locomotion (change in place), a change in quality and a change in quantity. For example, planets moving around the sun are in motion around the sun as well and growth being a motion. However, this motion needs a mover and has to have been put in motion by a force or another object as nothing can move itself and movement cannot go on infinitely. Aquinas’ believed that for this to occur there must have been an unmoved mover (a first cause) and this is analysed in terms of potentiality and actuality – all potentiality is based on original actuality. Aquinas used the example that the burning of wood needs an actual fire for the burning to occur. Aquinas believed that the original unmoved mover or the original actuality was God. An issue that arises from this argument is infinite regress. However, with the example infinitely extending staff, he rules this out.
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