This is one possible answer:
" Aquino expresses in this passage that can prove the existence of an absolutely necessary, that it is impossible not to be- from the observation that everything around us is contingent-that is, that may or may not be. It is the third of his way to the demonstration of the existence of God, which concludes that God call themselves the necessary same.
The argument of this pathway holds the remaining inductive scheme, using the following steps:
a) Starting point: finding things that we know can exist or not exist, ie they are contingent, so have begun to exist, indicating that some may not have existed.
b) Application of the principle of causality: The above implies the existence of some may need to be because of the existence of contingent beings, otherwise, if everything were contingent, nothing would exist today.
c) Failure of an infinite series of causes: necessary beings take their need for other things necessary, but it is impossible to an infinite series of things needed to get their need for others, it would, but first be necessary, not necessary intermediate beings would not last.
d) Conclusion: therefore there must be a necessary being itself, which need not come from any other cause, but he himself is because of the need for everyone else. And this is called God. "
