Nicholas Everitt in The Non-Existence of God has some relevant comments about reasonable standards of proof that are relevant to some of my recent posts:
“But we should not approach this search for reasons with unrealistically high expectations. We need to recognize that reasons can vary in strength. At one extreme, there will be those which provide absolutely conclusive support for (or against) a position. At the other extreme, will be reasons which raise (or lower) by only a minute amount the probability that our conclusion is true. In between, there will be reasons which can be ranged along a spectrum of strength. In ordinary life, we recognize the existence of this spectrum by deploying such locutions as:
A proves B beyond all doubt.
A is overwhelming evidence for B.
A is very strong evidence for B.
A makes B more likely than not.
A is good evidence for B.
A is fairly good evidence for B.
A makes B a really possibility.
A suggests that B.
A is some evidence for B.
A is weak evidence for B.
A marginally increases the likelihood that B.
The reason for emphasizing this spectrum is in order to remind ourselves that in the philosophy of religion, as elsewhere in daily life, being guided by reason does not mean demanding ‘proof’ before we can accept anything as true. The term ‘proof’ can of course be interpreted in many ways, but we rightly (i.e., reasonably or rationally) believe many things which we cannot prove. For example, I believe that my car will start when I next turn on the ignition and starter switch. This is a rationally defensible belief (the car has been very reliable in the past, it is regularly serviced, it is kept in a locked garage so is very unlikely to be interfered with, etc.). But the evidence that I have, good though it is, cannot be said to prove that the car will start next time. Nor would I be being rational or reasonable if I said, ‘I cannot prove the matter either way, therefore I cannot form any defensible view on the matter.’
In a similar way, being guided by reason in debates about God does not consist in refusing to accept anything until it can be proved. It is adjusting one’s beliefs in the light of the evidence that is available.” (The Non-Existence of God 13)