When we say someone is honest, we are comparing him or her to he or she who is most honest. If this is true, then we must compare all things to that which is most honest, good, noble, etc. Some being must be the perfection of all these things, for otherwise there would be no means of comparison.
Aquinas" fifth way is taken from the view that everything in this world acts for some purpose. He says we know this by their "acting always, or nearly always, in the same way, so as to obtain the best result." Therefore, we can infer that it is not accidental, but rather "designed" for these things or beings to serve their purpose. However, as pointed out in all of the previously stated arguments, nothing can give purpose to itself. An intelligent being must exist by whom all natural things are made for a certain purpose.
Although Aquinas brings up some very valid points in his argument for the existence of God, there are also some compelling objections to his theory. For instance, one might question the existence of a God that is wholly and infinitely good when there is evil in the world. It is hard to conceive of a being with infinite goodness existing while cruelty and immorality exist simultaneously. If "one of two contraries be infinite, the other would be altogether destroyed." So, if infinite goodness exists, it is impossible for evil to exist at all. However, his reply to this objection is also convincing. He says God's omnipotence and goodness are powerful enough to "allow evil to exist, and out of it produce good.".
The second objection to his philosophy is one that states that all natural things can be reduced to the principle of nature, and all things that happen intentionally can be reduced to the principle of human will, or reason. Given that these are the answers to which most people would turn to God for, to serve as an explanation for the ways of the world, this would give just cause to believe there is no God.
