One cause of misery and vice is always present with us in the greed and pride of men, but at certain periods in history this is greatly increased by the temporary prevalence of some false philosophy. Correct thinking will not make good men of bad ones; but a purely theoretical error may remove ordinary checks to evil and deprive good intentions of their natural support. An error of this sort is abroad at present. I am not referring to the Power philosophies of the Totalitarian states, but to something that goes deeper and spreads wider and which, indeed, has given these Power philosophies their golden opportunity. I am referring to Subjectivism.
After studying his environment man has begun to study himself. Up to that point, he had assumed his own reason and through it seen all other things. Now, his own reason has become the object: it is as if we took out our eyes to look at them. Thus studied, his own reason appears to him as the epiphenomenona which accompanies chemical or electrical events in a cortex which is itself the by-product of a blind evolutionary process. His own logic, hitherto the king whom events in all possible worlds must obey, becomes merely subjective. There is no reason for supposing that it yields truth.
As long as this dethronement refers only to the theoretical reason, it cannot be wholehearted. The scientist has to assume the validity of his own logic (in the stout old fashion of Plato or Spinoza) even in order to prove that it is merely subjective, and therefore he can only flirt with subjectivism. It is true that this flirtation sometimes goes pretty far. There are modern scientists, I am told, who have dropped the words truth and reality out of their vocabulary and who hold that the end of their work is not to know what is there but simply to get practical results. This is, no doubt, a bad symptom. But, in the main, subjectivism is such an uncomfortable yokefellow for research that the danger, in this quarter, is continually counteracted.
But when we turn to practical reason the ruinous effects are found operating in full force. By practical reason I mean our judgement of good and evil. If you are surprised that I include this under the heading of reason at all, let me remind you that your surprise is itself one result of the subjectivism I am discussing. Until modern times no thinker of the first rank ever doubted that our judgements of value were rational judgements or that what they discovered was objective. It was taken for granted that in temptation passion was opposed, not to some sentiment, but to reason. Thus Plato thought, thus Aristotle, thus Hooker, Butler and Doctor Johnson. The modern view is very different. It does not believe that value judgements are really judgements at all. They are sentiments, or complexes, or attitudes, produced in a community by the pressure of its environment and its traditions, and differing from one community to another. To say that a thing is good is merely to express our feeling about it; and our feeling about it is the feeling we have been socially conditioned to have.
–C.S. Lewis, from “The Poison of Subjectivism” in Christian Reflections (Eerdmans: Grand Rapids, 1967), p. 72