Good point--I think most faithful believers -believe in- the 'circular logic' because their faith leads them to believe in just that: circular logic, which is illogical, to the ordinary mind.  I can equate it to the belief that I can feel love.  But, really, there is no scientific proof of love, only evolutionary human behavior, and physiological human response mechanisms. So how can I prove that I feel love (if I do)? Well, because..I say so, that's why.  But why? Well, because...I feel it.  Can I prove it? Nope. Do I feel it? Yes, as surely as I feel, I feel love (and anger & other emotions), but in reality, scientifically, I have nothing to base any proof of those emotions on. I only have physiological/evolutionary responses, and they don't prove that feeling, only the responses to that feeling. So if I can't see it, or prove it, or put it in a box, does it really exist? I believe that it does.