Proof by contradiction is an effective
means of proof but its not the only
The best way
? One has to distinguish logical argument
. (Ironically, I got that point was a very radical but intelligent young earth creationist Jason Lisle).
Best Logical Argument:
The best logical argument for the non-existence of God, like all theistic arguments is probabilistic
1. Establish the inherent unproveability of the God concept. This effectively involves realizing that we see only natural occurences and that we don't know the full set of "natural" events. It is therefore logically impossible for us to ever objectively postulate the supernatural or even comprehend what the term means. At best we can have answerable questions
which one can interpret as "sign posts" to the supernatural but for which natural explanations may also exist with the axiom that matter existed in some form or other forever. We can't even prove that a given event happened in a permanent way.
2. Having established that it is philosophically impossible to have an objective reason to establish theism as a best explanation, one discusses Russel's tea pot story about the burden of proof.
3. One can use history
to show that man kind has a tendency to make up odd religious claims without any objective evidence for any of them.
Weaknesses in the above.
1. We can still "guess" what the natural laws are. We have some idea what we think most of them are. Quantum mechanics is the oddest
2. We can't prove a negative objectively. We are not proving that the books of the bible are not true accounts. They could be. (Noted we could go through the trouble to find weaknesses in them but the counter might be that the real details were lost in the sands of time).
3. We can't answer the unanswerable.
Most Persuasive Argument:
I don't know what is the most persuasive argument for non-God. Proably the argument of suffering
. Oddly, theists don't deny suffering and suffering doesn't conflict with their God's world view.
But theists often see God as being loving in a human sense of the word loving.
As an example, one of the pastors I knew, a person I rather liked, lost his son to suicide
. This seems to be shattering his personal faith.