If there be a God, there is no other fact in the world of such awful or such blessed import to man. Religion is based on faith that there is a God. To tell the religious mind that there is no scientific proof of the existence of God is to tell it nothing new. Those were not the terms on which we took up our faith—that we should have scientific proof of everything before we did anything. On the contrary, religion begins when, and only when, a man begins "to walk humbly with his God," to know that he knows nothing except that his soul cleaves to God and humbly trusts in Him. We do not bargain so much belief, and no more, for so much proof: we give "ourselves, our souls and bodies." The gift is free. The soul shrinks from saying even that it has proof of God's existence; it only knows it hopes and longs for Him. "Faith is the assurance of things hoped for," and the strength of our assurance is as the strength of our hope. But scientific proof is not the thing hoped for: it is not what is desired when the soul is conscious of but one thing, that it thirsteth, like the hart after the water-brooks, for the living God. The humble confession of our illimitable ignorance is the foundation of our faith and will ever be its sure refuge, its inexpugnable stronghold. It is only when, being ignorant, we are tempted to deny our ignorance, that trouble begins. We drop the substance for the shadow when we believe not in God, but in some proof of God.
To the man of science all this talk about faith appears mere folly, sheer unreason, a morbid wallowing in ignorance from pure love of ignorance; and there are others who, whilst admitting that proof is not what is wanted by some minds, yet are aware, from their own sad experience, that other minds yearn for it, and can know no peace without it. And if we ask what kind of proof it is that they require, the answer is plain: it is the same kind as science insists on. Then let us go to the man of science and wait at his door: he at any rate is not ignorant, and we, if ignorant, at least are willing to learn. That he should rather look down upon us is only what might be expected in a man who by sheer force of reason has discovered the sole source of truth and built up the whole fabric of science. Certainly, when he has taken us over his palace and shown us its marvels—the balances he uses to weigh the sun, the plates with which he photographs invisible stars, the cinematographic pictures of the earth's past history, his forecasts of the future of the solar system—we are not merely willing but eager to learn how it is all done. And when we come to know him, we find that in spite of the marvels, all of his own making, by which he is surrounded, he is not puffed up, as he might have been: indeed he is, he assures us, only an ordinary man. "Scientific investigation is not, as many people seem to suppose, some kind of modern black art."[25] It is simply plain, ordinary common sense, consistently applied; and, above all, persistently declining to accept anything without sufficient evidence. In ordinary life, says the man of science, we do not swallow any statement that anybody chooses to make—we ask for some evidence; and if science waxes every day, and religion wanes, it is merely because science has made it the rule of her being never to believe anything without sufficient evidence, and religion has not.
Naturally, then, we wish to know what is "sufficient evidence" in the eyes of science, since everything, we are told, depends on that. The reply is brief: whatever is based on the Uniformity of Nature has sufficient evidence. If we are inclined to be puzzled by the "Uniformity of Nature," we are soon reassured; it is literally the most ordinary thing in the world, there is no difficulty about it. Man is born into a world in which changes are unceasingly taking place. Some things change even as the clouds shift—every second, and in a way patent to all beholders. Others change imperceptibly and with great slowness, as e.g. the level of the dry land or the shape of the coast-line. But all things change, πάντα ῥεῖ. Nothing abideth long in one stay. It is these changes which bring all things good to man, and also all things ill. If, then, man is to survive, he must learn to evade the latter changes, which threaten to crush him, and he must be there in time to profit by the former. Such was the problem presented to primitive man, and such it still is for every one of us to-day: the successful man is the one who is beforehand with the world, and, if he is beforehand it is because he has learned to read the signs of the times and the seasons. In a word, he has learned to recognise that changes are not always mere chances, that some changes are uniformly preceded by certain others, and may consequently be foreseen. In the beginning the changes that man can forecast are few indeed: his prevision is no greater than the brute's. The child does not foresee that fire will burn; he learns by experience. And whatever man can forecast, he has learned it all by experience. It is a slow way of learning, it has taken man thousands upon thousands of years to learn what he knows now; still he has learned to know the causes of countless things, to control the causes and to anticipate the effects of many. But more important, more valuable than all his experience and all his knowledge of what produces what, of what uniformly precedes or follows what, is the final and comprehensive truth which at last he reaches, that nothing happens arbitrarily, that everything in nature is uniform. That, the Uniformity of Nature, is the great truth in which all others are summed up: to its establishment have gone the labours of all past generations of mankind, to its support the whole experience of the race contributes. It is the truth of truths, the test of truth: whatsoever is established on it shall not be shaken, whatever contravenes it shall not endure.
The Uniformity of Nature is the base not only of all science, but of every act of reason in the most commonplace affairs of ordinary life; and, though you may not know it, you assume it every moment. Why are you sure that the sun will rise to-morrow? Because Nature is uniform. Why do you know that fire will burn? Because Nature is uniform. Why that all men are mortal? Why that a cause will always produce its effect? Because of the Uniformity of Nature. For each and all of these beliefs the evidence is sufficient; it is the Uniformity of Nature. How different, says the man of science, is the procedure of science, that is of common sense, from the unscientific methods of theology! Why do we believe that the earth will bring forth her kindly fruits in due season? Because it is God's will? That is a hypothesis; it may be true or it may not; it cannot be proved or disproved; there is no evidence against it, but there is no evidence for it. Very different is the answer of science and common sense: it is that the earth will produce crops in accordance with certain natural causes, mechanical and chemical. That also is a hypothesis which may or may not be true. Yes, but it is one for which there is some evidence—the Uniformity of Nature. In the same way, if anyone were to say that the result of the next general election depended not on the electors but on the planets, we should decline to believe him, because there is no evidence to show that the planets have anything to do with it, and there is good evidence for believing that the votes of the electors have. In fine, the teaching of science is: demand sufficient evidence for everything, and always remember that by sufficient evidence is meant the Uniformity of Nature.
This sounds so simple and so convincing that we are tempted to try it. But first let us make sure that we have learned our lesson properly. In the course of long ages mankind has slowly accumulated enough experience to warrant the confident belief that Nature is uniform. Now, primitive man was of course a savage, and knew nothing of the Uniformity of Nature; he therefore could not have had sufficient evidence for believing anything in his experience. But it is on the accumulation of such experiences—every one of which we must reject because they were not based on the Uniformity of Nature—that our belief in the Uniformity of Nature is supposed to rest. In other words, it is based on them and they were based on nothing. This result of acting strictly up to the principle of not suffering anything to pass without sufficient evidence seems somewhat discouraging, until the man of science comes to our rescue and reminds us that just as we, without knowing it, have acted all our lives on the tacit assumption that Nature is uniform, so did primitive man; and that consequently there really was sufficient evidence and scientific proof for the savage's experiences, though of course he could not have framed it in words; and so, the bases of the Uniformity of Nature are really quite sound. But even now we are not altogether out of our difficulties, for granted that the savage, like ourselves, tacitly assumed Nature to be uniform, was there sufficient evidence for the assumption? and if so, what was the evidence? It could not be the Uniformity of Nature, because that is just the question; and, if it was anything else, it was not sufficient evidence.
It really seems rather difficult to get sufficient evidence for the axiom, viz. the Uniformity of Nature, on which the whole of science is built. And yet we must have sufficient evidence for it, or else we shall have to conclude that Science has no more logical foundation than Religion.
But once more the man of science comes to our assistance and explains that in the beginning, before the Uniformity of Nature is proved, it is only probable that what has once happened will happen again in similar circumstances, and at first perhaps not very probable; but when wider and wider experience still shows that what has once happened does actually happen again under the same circumstances, the Uniformity of Nature becomes more and more probable, until at last, if not actually proved, it is still the most probable hypothesis that we possess or can possess: "our highest and surest generalisations remain on the level of justifiable expectations; that is, very high probabilities."[26]
Now, with all respect to logicians like John Stuart Mill, and men of science like Huxley, we must point out that this begs the whole question. If we assume that Nature is uniform, then it is probable that what has often happened will happen again. But if we do not assume that Nature is uniform, then the repeated occurrence of a thing does not make it in the least probable that it will occur again. To assume without proof that Nature is uniform is to ask us to accept a statement without evidence, which, if we have learnt the lesson of science, we can hardly do. On the other hand, if we begin with the admission that Nature may or may not be uniform, but that, to begin with, we no more know whether it will actually prove to be uniform than we know whether a penny, when we are about to toss it, will fall head or tail; then, according to the mathematical theory of probability, it matters not how many times you toss the penny, the chances next throw are exactly the same as they were at the first throw—it matters not how many times Nature has proved uniform in the past, she is no more likely to prove uniform to-morrow than she was on the first of days. If it is really an open question at the beginning whether Nature is or is not uniform, it remains an open question to the end. The man of science need not admit that it is an open question, if he does not want to do so; but if he does admit it, then let him stick to it throughout; and let him reflect that if he begins by admitting it and ends by denying it, he has but gradually retracted his own free admission, and unconsciously been betrayed into denying what he began by admitting to be true.
The fact of the matter is that the axioms of science—the Uniformity of Nature and the Law of Universal Causation—not only are not proved by what experience we have had of them, but "cannot be proved by any amount of experience."[27] Not only can they not be proved by any amount of experience, they are incapable of being demonstrated at all: "they are neither self-evident nor are they, strictly speaking, demonstrable."[28] If, then, they are not and cannot be proved either by experience or in any other way, on what does the man of science ground his belief in them? On Faith. "The ground of every one of our actions, and the validity of all our reasonings, rest upon the great act of faith, which leads us to take the experience of the past as a safe guide in our dealings with the present and the future."[29]