Double Think
We are guilty of double think (a concept which Barfield borrows, of course, from George Orwell's 1984 [1949]) whenever we hold two completely incompatible, indeed contradictory, ideas in the mind simultaneously without noting the contradiction. Barfield finds double think prominently displayed in our present tendency to "think that what physics tells us is true, is true when we are studying physics, and untrue when we are studying something else" (SA 38).

"Our age," Barfield observes, "is characterized by a variety of generalizing theories, each of which is applied to everything in the universe except itself, and each of which would fall to the ground if it were so applied since it at once becomes apparent that it has been busy sawing off the only possible branch on which it could have been sitting" (OC 603). "It is a failing common to a good many contemporary metaphysical theories," he had noted as early as Poetic Diction,

that they can be applied to all things except themselves but that, when so applied, they extinguish themselves; and experience has taught me that, when men are really attached to such a theory, most of them will, after this has been pointed out to them, continue nevertheless to apply it to all things (except itself). (16)
Nowhere is double think more apparent than in the epistemology of the sciences, as Barfield explains in Worlds Apart. For scientists
have now got hold of this method of knowledge, which by definition, excludes man and all his values from the object to be known and they have found it very useful. But not content with this, they go on insisting that the method itself has a human value and enhances human dignity. They are like children thinking they can have it both ways. First, they insist on cutting out awe and reverence and wisdom and substituting sophistication as the goal of knowledge; and then they talk about this method of theirs with reverence and awe and expect us to look up to them as wise and venerable men. (22)
Take the example of physics:
Having established the gulf which yawns between the atomic physical structure of nature and the appearances of the physical world, it is of course possible, it is certainly usual--if we are physicists, to continue undisturbed with our investigations of the unappearing atomic structure, and, if we are philosophers, to leave it at that, being content with the metaphysical curiosity we have produced. It is usual; but it is not really necessary to do so. We could, if we chose, take it seriously; we could keep the gulf steadily in sight, instead of instantly forgetting all about it again, and see what effect that has on our knowledge of other things, such as the evolution of nature and of man himself. (SA 12-13)
In one sense, double think is simply the product of intellectual laziness. After all, "It is much more convenient, when we are listening to the geologist, to forget what we learnt about matter from the chemist and the physicist" (SA 23). But double think has deeper roots; it underpins the idolatry of the age. Abandonment of double think will therefore prove to be a decisive step in the evolution of consciousness.
The way out may still lie through and not back. The best way of escape from deep-rooted error has often proved to be, to pursue it to its logical conclusion, that is, to go on taking it seriously and see what follows. Only we must be consistent. We must take it really seriously. We must give up double-think. For inconsistent and slovenly thought can abide indefinitely in error without any feeling of discomfort. (SA 57)
See in particular Worlds Apart, passim, Saving the Appearances, Chaps. VII, VIII.