It would seem, from all this, that so long as we are keeping to the scientific point of view, that is to say, taking for granted that there is something objectively real answering to our perceptions and conceptions, the question of the possibility of a universal or (permanently) common illusion does not arise.  Yet a little more reflection will show us that it may arise in a way.  So far as the logical sufficiency of the social consensus or common belief is accepted as scientifically proved, it is open to suspicion on strictly scientific grounds.  The evolutionist’s proof involves one or two assumptions which are not exactly true.

In the first place, it is not strictly correct to say that all illusion involves a practical unfitness to circumstances.  At the close of our investigation of particular groups of illusion, for example, those of perception and memory, it was pointed out that many of the errors reviewed were practically harmless, being either momentary and evanescent, or of such a character as not to lead to injurious action.  And now, by glancing back over the field of illusion as a whole, we may see the same thing.  The day-dreams in which some people are apt to indulge respecting the remote future have little effect on their conduct.  So, too, a man’s general view of the world is often unrelated to his daily habits of life.  It seems to matter exceedingly little, in general, whether a person take up the geocentric or the heliocentric conception of the cosmic structure, or even whether he adopt an optimistic or pessimistic view of life and its capabilities.

So inadequate, indeed, does the agency of natural selection seem to be to eliminate illusion, that it may even be asked whether its tendency may not be sometimes to harden and fix rather than to dissolve and dissipate illusory ideas and beliefs.  It will at once occur to the reader that the illusion of self-esteem, discussed in the last chapter, may have been highly useful as subserving individual self-preservation.  In a similar way, it has been suggested by Schopenhauer that the illusion of the lover owes its force and historical persistence to its paramount utility for the preservation of the species.  And to pass from a recurring individual to a permanently common belief, it is maintained by the same pessimist and his followers that what they regard as the illusion of optimism, namely, the idea that human life as a whole is good, grows out of the individual’s irrational love of life, which is only the same instinctive impulse of self-preservation appearing as conscious desire.  Once more, it has been suggested that the belief in free-will, even if illusory, would be preserved by the process of evolution, owing to its paramount utility in certain stages of moral development.  All this seems to show at least the possibility of a kind of illusion which would tend to perpetuate itself, and to appear as a permanent common belief.

Now, so far as this is the case, so far as illusion is useful or only harmless, natural selection cannot, it is plain, be counted on to weed it out, keeping it within the narrow limits of the exceptional and individual.  Natural selection gets rid of what is harmful only, and is indifferent to what is practically harmless.