There is an interesting piece of conversation between the Archbishop and La Trémouille in Bernard Shaw’s Saint Joan. It goes like this:

LA TRÉMOUILLE: Well, come! What is a miracle?
THE ARCHBISHOP: A miracle, my friend, is an event which creates faith. That is the purpose and nature of miracles. They may seem very wonderful to the people who witness them, and very simple to those who perform them. That does not matter: if they confirm or create faith they are true miracles.
LA TRÉMOUILLE: Even when they are frauds, do you mean?
THE ARCHBISHOP: Frauds deceive. An event which creates faith does not deceive: therefore it is not a fraud, but a miracle.

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