The First Way of Thomas Aquinas

Utrum Deus Sit

Pt 1. The Argument from Motion

​The first and a very clear way is taken from motion.
It is certain, and the senses confirm, that some things in the world move.
Everything, however, that moves, is moved by another. This is because nothing moves except insofar as it is in potency to that toward which moves, but something moves another insofar as it is itself in act. Nothing can be reduced from potency to act except through something already in act. Accordingly, something hot in act – such as fire – makes wood – which is hot in potency – hot in act. Through this actuality, fire moves and changes the wood. It is not possible however, that something is both in act and in potency at the same time and with respect to the same thing, but only with respect to different things. For what is actually hot cannot also be potentially hot, but it can be potentially cold. It is therefore impossible that a thing is both a mover and moved with respect to the same motion, or that something moves itself. Everything in motion must be moved by another.
If that which moves is itself moved by another moving thing, then that other must itself be moved by another and that by another. This cannot proceed to infinity, however, because there would be no first mover, and so there would be no other movers. This is because nothing moves unless it is moved by a first mover, just as the staff does not move unless the hand moves it.
It is therefore necessary to arrive at some first mover, and all understand this to be a god.

First, to understand this argument, it is necessary to touch on the principle that nothing gives what it does not have. If I don’t have $100, it is utterly impossible for me to give you $100. Similarly with every form, every facet of existence and every perfection, if something does not have it, it cannot cause something else to have it. The entirety of Aquinas’s philosophy stands or falls with this axiom. This is reflected in the first way, “Nothing can be reduced from potency to act except through something already in act.” In other words, if something is changing, it must be operated upon by an agent already in possession of the term of the change. If a hot ball is thrown into a bucket of cold water, the water heats up because the ball is already hot.

Moreover, “It is not possible that something is both in act and in potency at the same time and with respect to the same thing, but only with respect to different things.” Put succinctly, you cannot become what you already are. A child is in potency to manhood insofar as he is able to become a man. Once the child has become a man, he is no longer able to become a man. He already is one.

At this point it is worth noting that Aquinas is not speaking here of locomotion specifically. In his mind there are four types of motion: locomotion, qualitative motion, quantitative motion, and generation & corruption. In each case, motion is a becoming. If it is helpful, one can replace “motion” with “becoming” or “change”. Because a thing cannot become what it already is, motion requires that the term of the motion is only imperfectly possessed by the moving thing.

“It is therefore impossible that a thing is both a mover and moved with respect to the same motion, or that something moves itself.” The reason for this is clear. The mover must posses the term of the motion to a greater degree than the mobile itself has it. For a ball of iron to heat water, the iron must be hotter than the water. Nothing can posses anything to a greater degree than itself, however. This would be a direct contradiction.
Thus, Aquinas concludes, “Everything in motion must be moved by another.” He could just as well have said, “Everything is changed only by something more in act than itself with respect to the term of the change.”

If that which moves is itself moved by another moving thing, then that other must itself be moved by another. This cannot proceed to infinity, however, because there would be no first mover, and so there would be no other movers. This is because nothing moves unless it is moved by a first mover, just as the staff does not move unless the hand moves it.

Undoubtedly, this is the part of the argument that trips up the most philosophy students nowadays. There can’t be an infinite regress why exactly? Because there would be no first mover? So, there can’t be an infinite regress because you can’t have an infinite regress…? Is this not replacing an infinite regress with circular reasoning?

Actually, no. No it isn’t.

That there can be no infinite regress follows directly from what had already been laid out. A moving thing is always in potential with regard to the term of the motion. What is in potential is only reduced to act by what already is in act. If nothing actually possesses the term of the motion, then that simply is not the term of the motion. If something is moving, it has to be moving toward whatever is sharing its own act. But, of course, if something is already in act with reference to the term of a motion, it can only be a mover in that motion; it cannot itself be moving into what it already is. Therefore, there cannot be an infinite regress. The series of movers must finally come to one first moved thing and one unmoved mover.
​
“All understand this to be god” By definition, this unmoved mover is the term of every motion. It is literally the perfection toward which everything moves. How could it not be god?

Prima autem et manifestior via est, quae sumitur ex parte motus. Certum est enim, et sensu constat, aliquia moveri in hoc mundo. Omne autem quod movetur, nisi secundom quod alio movetur. Nihil enim movetur, movet autem aliquid sdcundum quod est actu. Movere enim nihil aliud est quam educere aliquid de potentia in actum, de potentia autem non potest aliquid reduci in actum, nisi per aliquid ens in actu, sicut calidum in actu, ut ignis, facit lignum, quod est calidum in potentia, esse actu calidum, et per hoc movet et alterat ipsum. Non autem est possibile ut idem sit simul in actu et potentia secundum idem, sed solum secundum diversa, quod enim est calidum in actu, non potest simuil esse calidum in potentia, sed est simul frigidum in potentia. Impossibile est ergo quod, secundum idem et eodem modo, aliquid sit movens et motum, vel quod moveat seipsum. Omne ergo quod movetur, oppertet ab alio moveri. Si ergo id a quo movetur, moveatur, opportet et ipsum ab alio moveri et illud ab alio. Hic autem non est procedere in infinitum, quia sic non esset aliquod primum movens; et per consequens nec aliquod aliud movens, quia moventia secunda non movent nisi per hoc quod sunt mota a primo movente, sicut baculus non movet nisi per hoc quod est motus a manu. Ergo necesse est devenire ad aliquod primum movens, quod a nullo movetur, et hoc omnes intelligunt Deum.