The cosmological argument, or the first cause argument, centers around the belief that the universe had a first cause. It is based on an a posteriori premise, which means that the argument is taken from experience of what can be seen around the world and universe. The word cosmos refers to the universe as a well ordered system, a belief this argument rests upon. A common feature in all the versions of this argument for the existence of God is their need for a beginning of either the universe or the systems within the universe. Many associate this "beginning" with the word "God". .
The philosopher Plato questioned " How can a thing that is moved by another ever be the beginning of change?" Plato related this to processes within the universe of motion or change and their need for a beginning then translated this view for the creation of the universe concluding there was a need for a "motion which can move itself". Aristotle, Plato's pupil, carried forward the cosmological argument combining it with religion around 360 BC. .
Thomas Aquinas (1225-1274) was the most influential philosopher in the development of the cosmological argument. He was convinced there were features of the world that could prove the existence of God. In Aquinas's first way he talks of motion. However by this he does not simply mean physical motion but more the concept of change. Through observation Aquinas deduced that "Whatever is moved must be moved by another" but he does not agree with the idea of infinite regress: that there could have been no beginning, that this was some infinite chain of motion. This first way talks on the ideas of potentiality and actuality, as are illustrated in this famous fire/wood example. The wood if potentially hot whilst the fire is actually hot. Aquinas was making the point that the wood could not initiate the change therefore an "unmoved mover" is needed "and this everyone understands to be God" .