But did he not by some magical metamorphosis turn these probabilities into a certainty? No; he simply claimed that they were sufficient to produce certitude, which is a different matter. Certitude, he held, was a quality or habit of mind; certainty, a quality of propositions; and probabilities that did not reach to logical certainty might suffice for a mental certitude. We are mentally sure almost every day of many things which could not be demonstratively proved; we are practically as sure of them as if they could be proved; we are ready to act on the basis of them, and that is the test of practical certitude. The word of a friend on a matter of which we are ignorant is an example; we may be as sure of what he tells us as if we had seen it ourselves; yet he may be mistaken; strictly speaking, his word is only probable evidence. But did not Newman substitute faith for reason? Yes, in a sense; but not in a sense in which it is of itself irrational to do so. How much could the reason of any of us tell us of Central Africa? We know of it by testimony, do we not? not by reason. From our own notions alone we could not tell whether it was a desert or a forest; whether it was inhabited or uninhabited; whether full-grown human beings or dwarfs lived there; but a Livingstone, a Du Chaillu, a Stanley, tell us, and we accept their word. The fact is, that trust in testimony is what we daily practise. We learn of what is going on in a neighboring town, of much in our own town, of much in our own house (unless we are there all the time, and in every part of it at the same time) not by reasoning about it, any more than by sight, but by faith in what others tell us. "Why should we be unwilling to go by faith?" asks Newman. "We do all things in this world by faith in the word of others. By faith only we know our positions in the world, our circumstances, our rights and privileges, our fortunes, our parents, our brothers and sisters, our age, our mortality; why should religion be an exception? Why should we be willing to use for heavenly objects what we daily use for earthly?" There is really nothing mystical about faith; it is not peculiarly a religious principle, nor is it the ideal way of getting knowledge. As Newman says, "The word of another is in itself a faint evidence compared with that of sight or reason. It is influential only when we cannot do without it."