At OzAtheist, Christopher asks:
If it could be shown, through logic, that God, as you both have defined him [or her, or it], exists then would that be considered sufficient reason to justify belief?
My response follows . . .
I should reiterate that I don’t think you can use logic as a source of truth about the world and the universe, and therefore I don’t think arguments that rely upon logic alone–that is, to the exclusion of evidence–could ever be considered sufficient reason to justify belief.
I’ve used the following example in a discussion with SS2 in another thread, but it bears repeating here. Let’s take President Bush’s famous 2001 statement “Either you are with us, or you are with the terrorists,” and restate it in logical terms:
P1. Either you are with us, or you are with the terrorists.
P2. You are not with us.
C. Therefore, you are with the terrorists.
The argument above is deductively valid: as long as the premises are true, the conclusion will be true. But it is also factually wrong, It is possible to be neither with us nor with the terrorists, and as a matter of fact many nations and individuals, both with the Western world and without, both within the US and without, were neither supporters of the terrorists nor uncritical supporters of the policies of the Bush administration.
But it is very easy to see how some people could become bamboozled by the deductively valid form of the President’s argument (once you add in the implied P2 and conclusion), and confuse validity with truth. What they miss is that logic is only truth-preserving; it is not inherently true. Since we are not talking about mathematics here, and since by “true” I mean “true about the world and the universe,” there must be provided sufficient supporting evidence to justify the belief that P1 and/or P2 are true. (”True,” that is, in the tentative sense of being true only until there is sufficient evidence to justify the belief that P1 and/or P2 are in fact false, and so on.)
You’ve heard of the adage, popularised by Carl Sagan, that “extraordinary claims require extraordinary evidence.” Whether it is capital “T” true is one thing; it certainly has and does work as a useful guiding principle for establishing (albeit tentatively, but tentatively is probably the best we can do) truths about the universe. Well, the claim that a deity/deities/the supernatural exists is surely an extraordinary claim, and my position all along in this thread has been that it would take extraordinary evidence–so extraordinary that I am having difficulty even imagining what it could look like–to convince me to accept this claim. I certainly don’t think ordinary evidence–e.g. anecdote, scriptures, personal testimonies, etc.–is up to the task. So why, then, would I be justified in accepting the extraordinary claim that a deity/deities/the supernatural exists with no supporting evidence whatsoever?
So, to sum up, this is how I see the suggestion that I would be justified in accepting this extraordinary claim on purely logical grounds:
P1. If I have a bridge to sell you, you ought to buy my bridge.
P2. I have a bridge to sell you.
C. Therefore, you ought to buy my bridge.
Sorry, but I need to see this bridge–or be provided with sufficient evidence of its existence–before I consider buying it.
BTW, as long as we’re on the subject . . .