For this argument, we are defining God as the "greatest possible being." As the greatest possible being, God is by definition a necessary being. A necessary being is by definition a being that must exists if its existence is possible.
#1 If it is possible that God exists, then God exists
#2 It is possible that God exists
#3 Therefore, God exists
"You cannot be serious!" is probably what you are thinking, but the argument might surprise you even if it does not convince you. The argument is valid, meaning the conclusion follows from the
premises. The only way to argue against the conclusion is to challenge
the premises. Almost everyone, including most atheists, would agree
with premise #2 (at least initially). So the whole argument falls on
premise #1. But as stated above, if God did exist He would be the
greatest possible being, and the greatest possible being would have the
attribute of necessity, and something that is necessary exists if it's
existence is possible. Sounds like a stretch? It it is interesting that this is relatively uncontroversial because
one definition simply leads to the next. But if premise #1 is true,
then the only way to deny the argument is to go back and deny premise
#2. An opponent of the argument must show that the concept of God is
incoherent or otherwise impossible. Otherwise, the argument is sound and
the conclusion is true. Or at least, so goes the argument.
Strengths:
- Most skeptics would say that God probably does not exist. But to say that God probably does not exist is just to say that God possibly exists and therefore concedes premise #2.
- The argument makes the issue black or white - God's existence is either true or impossible.
- If successful, the argument poses a few interesting situations. For instance every agnostic alive would have to believe that God exists in order to be consistent with agnosticism, thereby contradicting himself.
Weaknesses:
- The argument is very abstract (and silly to some) and consequently hard to take seriously.
- It is easy to deny premise #2, which is what most opponents of the argument do.
- The argument does not argue for Christianity as revealed by Jesus, but only for the greatest possible being.
- Psalm 14:1, 53:1, 145:3