You may discourse for hours upon the Laws of Nature, but you will never succeed in convincing any one, not even yourself, that they will remain valid in the moment that is to come, by the mere force of logic. You are certain—so am I practically quite certain—that the stone which I throw at this moment up in the air, will, in the next moment, fall to the ground. But this certainty does not arise from logic. We have absolutely no reason for this leap into the darkness of the future except faith,—faith of course resting upon a basis of facts, but still faith. The very names and notions of “cause” and “effect” are due not to observation, nor to demonstration, but to faith. The name, and the notion, of a Law of Nature are nothing but convenient ideas of the scientific imagination, based upon faith. Take an instance. We say, and genuinely believe, that fire and gunpowder “cause” explosion; that explosion is the “effect” of gunpowder and fire; and that the effect follows the causes in accordance with the “laws of nature;” but you have not observed all this and you cannot demonstrate it. You have merely observed in the past an invariable sequence of explosion following (in all cases that you have seen or heard about) the combination of gunpowder and fire; you have also perhaps predicted in the past that explosion would follow, and demonstrated that it did follow this combination, as often as you pleased; you have found, or have heard that others have found, that this sequence agrees with other chemical sequences, which you are in the habit of calling causes and effects; but all this is evidence as to the past, not as to the future. Your certainty as to the future arises not from any demonstration about the future, but from your faith or trust in the fixed order of Nature, and from nothing else. Now the greater part of the action of life deals with the future. It follows therefore that, in the greater part of life, we act, not from demonstration, but from a proof in which faith is a constituent element.
Whence arises this trust in the uniformity of the phenomena of the Universe? We can hardly give any other answer except that we could not get on without it. Having been found to “work” by ourselves, and by many generations of our forefathers, this faith is possibly by this time an inherited instinct as well as the inbred result of our own earliest experiences. But when we analyse it we are forced to confess that we can give no logical account of it. Logically regarded, it savours of the most audacious optimism, arguing, or rather sentimentalizing, after this fashion: “It would be so immensely inconvenient if Nature were every moment changing her rules without notice! All forethought, all civilization would be at an end; nay, we could not so much as take a single step or move a limb with confidence, if we could not depend upon Nature!” Does not this personification of Nature, and trust or faith in Nature, somewhat resemble our trust or faith in God? I think it does; and it is very interesting to note that the very foundations of science are laid in a quasi-religious sentiment of which no logical justification can be given.