Russell's teapot, along with the Flying Spaghetti Monster, is supposed to be very improbable in the absence of strong evidence that it does exist, and since we should consider the existence of a floating teapot to be highly improbable initially, we should reason in the same way for God.
We do know that matter doesn't ordinarily arrange itself into the shape of a teapot unless there are persons around who want to heat and pour tea. How this is supposed to bear on the probability of something existing which , ex hypothesi, is not derived from natural processes, is something I don't understand.
