However this may be, there is nothing in the doctrine of “congruity” which should shock those who are jealous for the supremacy of reason and the dignity of science. It is science itself which assures us that all premises, all conclusions, and all the logical links by which they are connected must be regarded as natural products. It is science itself which assures us that they belong, like all natural products, to the tissue of causes and effects whose lengthening web is continuously thrown off by the loom of time. It is science itself which requires us to harmonise these two aspects of the knowing process—the one logical and timeless; the other causal and successive.
But how are they to be harmonised if the causal series is fundamentally non-rational? Suppose yourself able to observe the development of beliefs in some alien being (say an inhabitant of Mars) as a bacteriologist observes a growing colony of microbes: suppose, further, that your observation showed how these beliefs arose from causes which had in them no tincture of reason, and that, so far as you could see, they were quite unsupported by any independent evidence which—for you—had weight or even meaning. Would you rate their value high? Surely not.
Now it is quite true that when we examine our own system of beliefs we cannot imitate this attitude of complete detachment, since in the very act of examination some of these beliefs are assumed. But we can examine the beliefs of other people, and we do, as a matter of common-sense practice, rate low the value of the beliefs whose sources we perceive to be non-rational. How, then, can we refuse to apply to ourselves a principle of judgment which we thus apply without scruple to our neighbours?
Whenever we do so apply it, we shall, I think, be forced to admit that all creeds which refuse to see an intelligent purpose behind the unthinking powers of material nature are intrinsically incoherent. In the order of causation they base reason upon unreason. In the order of logic they involve conclusions which discredit their own premises. Nor is there, as far as I can see, any mitigation of this condemnation to be looked for except by appealing to the principle of Selection. And how far will this help us out of the difficulty?
Just so far as an imitation of intelligent purpose can be a substitute for its reality, but no further. And how far is this? At first sight we might suppose that, at the worst, the cognitive series and the causal series might be harmonised on the basis of natural selection if knowledge never aspired to rise above the level which promoted race survival, if no faculties of knowing were trusted beyond the point where they ceased effectively to foster the multiplication of the species. Up to this point it would seem that, if selection be true, there is congruity between beliefs and their origin. The sequence of events which brought them into being suggests no doubt about their value. This scheme of thought, therefore, though narrowly restricted, is apparently coherent.
Yet even this modest claim must be deemed excessive: for the speculation on which it rests does violence to its own principles. Manifestly we cannot indulge ourselves in reflections upon the limits of the “knowable” without using our intellect for a purpose never contemplated by selection. I do not allege that our intellect is therefore unequal to the task. I only say that, if it be indeed equal to it, we are in the presence of a very surprising coincidence. Why should faculties, “designed” only to help primitive man, or his animal progenitors, successfully to breed and feed, be fitted to solve philosophic problems so useless and so remote? Why, indeed, do such problems occur to us? Why do we long for their solution?
To such questions Naturalism can neither find an answer nor be content without one. Wearied with unavailing efforts to penetrate the unknown, many not ignoble spirits have preached the wisdom of dulling unhealthy curiosity by the aid of healthy labour. “Let us cultivate our gardens” (they say), seeking no solution of the insoluble.
But the advice is ambiguous. Will the proposed remedy, in their opinion, cure the ill, or only help us to forget it? If the latter, then, in some circumstances and with some patients, it will doubtless fulfil its promise. Oblivion may be attained by growing vegetables, as by other less reputable expedients. But if absorption in daily labour be recommended as the final stage of a rational cure, it cannot be effectual. No rational cure is, on naturalistic principles, within our reach. Could we empty ourselves of all that makes us men, could we lower our intellectual level to the point where the scope of our mental activities harmonised with their naturalistic source, we should doubtless free ourselves from the malady of vain speculation. But though the remedy, if applied, would be effectual, it would not be rational. Reflective Agnosticism cannot be combined with scientific Naturalism, because reflective Agnosticism is the product of a process which Naturalism inevitably discredits. And if Naturalism be incompatible even with reasoned ignorance, how can we hope to harmonise it with the claims of reasoned knowledge?[16]
The best imitation of creative purpose, therefore, which Naturalism can provide breaks down where it is most required—namely, at the highest levels of value. I have just shown this in connection with our powers of thought, and the beliefs to which they lead. But the failure is not confined to them. It is as wide as Humanism itself. Wherever we find great intrinsic worth, there we are in a region where the direct effect of selection is negligible. The noblest things in speculation, in art, in morals, possess small survival value; and, though the geniuses to whom we owe them have added greatly to the glory of their race, they have added but little to its animal successes. In the language of these lectures, they are “accidental”—due neither to purpose nor to any arrangement of causes by which purpose is successfully copied.