I have heard it said over and over again that one cannot demonstrate the existence of God. Well, that is purely false. I have here the Five Ways offered by Aquinas, and not only do they demonstrate the existence of God, but they demonstrate the existence of a theistic God, one identical in all comparable ways to the one in Scripture. One downfall to these ways is that they were written in the 13th century, and the language use is sometimes archaic, but understandable but for a couple of terms, which I will clarify. Probably the best feature of these arguments is that they are presented in syllogism form, so if the premises are true, then the conclusion follows. If any of you would like to deny the conclusion of any of these arguments (that God exists), then deny a premise and we can have a hearty debate!
Way 1- The Argument from Motion (Change)
P1-It is evident that some things are in motion (are changing).
P2-Now, whatever is in motion (changing) must be put into motion (changed) by another, for nothing can be in motion (changing) except it is in potentiality to that towards which it is in
motion (changing); whereas a thing moves as much as it is actualized. For motion (change) is nothing else than the reduction of something from potentiality to actuality.
P3-But nothing can be reduced from potentiality to actuality, except by something in a state of actuality.
P4-Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects.
P5-It is therefore impossible that in the same respect and in the same way a thing should be both mover (changer) and moved (changed one); that it should move (change) itself.
P6- Therefore, whatever is in motion (changing) must be put into motion (changed) by another.
P7- If that by which it is put in motion (changed) be itself put in motion (has also changed), then this also must needs be put in motion (changed) by another, and that by another again.
P8-But this cannot go on to infinity, because then there would be no first mover (changer), and consequently no other mover (changer); seeing that subsequent movers move only inasmuch as they are put in motion (changed) by the first mover.
Conclusion-Therefore, it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.
Way 2- From the nature of efficient causes (causes of existence)
P1-In the world of sense we find there is an order of efficient causes (causes of existence).
P2-There is no case known in which a thing is found to be the efficient cause (cause of existence) of itself; for so it would be prior to itself, which is impossible.
P3-Now in efficient causes (causes of existence), it is not possible to go on to infinity, because in all efficient causes (causes of existence) following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or one only.
P4-Now, to take away the cause, is to take away the effect
P5-Therefore, if there be no first cause among efficient causes (causes of existence), there will be no ultimate, nor any intermediate cause.
P6-But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause,
neither will there be an ultimate effect, nor any intermediate efficient causes (causes of existence); all of which is plainly false.
Conclusion-Therefore, it is necessary to admit a first efficient cause, to which everyone gives the name of God.
Way 3- From Contingent (possible, dependent on another for existence) Beings to a Necessary
(independent of any other for existence) Being
P1-We find in nature things that are possible to be and not to be, since they are found to be generated (come into being), and corrupt (degrade to the point of death), and consequently they are possible to be and not to be.
P2-But it is impossible for these always to exist, for that which is possible not to be at some time is not.
P3-Therefore if everything is possible not to be, then at one time there could have been nothing in existence.
P4-Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing..
P5- Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence-which is absurd.
P6- Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary.
P7-But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have there necessity caused by another, as has already been proved in regards to efficient causes (causes of existence).
P8-Therefore, we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity.
Conclusion-This all men speak of as God.
Way 4- From Gradation (Degree of Value) In Things
P1-Among beings there are some more and some less good, true, noble, and the like.
P2-But "more" and "less" are predicated of different things, according as they resemble in their
different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest, and, consequently, something which is uttermost being, as it is written in Metaphysics ii.
P3-Now the maximum of any genus (class) is the cause of all in that genus (class)...
Conclusion-Therefore, there must be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.
Way 5- The Argument from Governance (design)
P1- We see that all things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way so as to obtain the best result.
P2-Hence it is plain that not fortuitously, but designedly, do they achieve their end.
P3-Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as an arrow is shot to its mark my an archer.
Conclusion-Therefore some intelligent being exists by whom all natural things are directed towards their end; and this being we call God.