(not meaning "demonstrated," but simply "made probable," or "proved for practical purposes").
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.
