Primary and Secondary Qualities
The philosophical question of the nature of primary and secondary qualities (modern philosophers from Descartes to Locke have made substantial contributions to the debate, though its origins are ancient)1 reveals the internalization process that shapes the evolution of consciousness in its present phase.

"Modern physics," Barfield shows in "The Rediscovery of Meaning," "originally set out to investigate nature as something existing independently of the human mind. . . ." It was, after all, the goal of science to render a detached, completely objective, view of the world. But this pursuit, driven, in part, by received wisdom on primary and secondary qualities, took a very strange epistemological turn:

At a quite early stage a distinction was made between "primary" qualities, such as extension and mass, which were assumed to inhere in matter independently of the observer and 'secondary" qualities like color, which depend on the observer.2 Roughly speaking, physics has ended by having to conclude that all qualities are "secondary" in this sense, so that the whole world of nature as we actually experience it depends for its configuration on the mind and senses of man. It is what it is because of what we are. (RM 17)

As Barfield reminds in an essay on "Science and Quality," "Ousted from nature, the qualities, whether occult or manifest, had to go somewhere. . . ." They went indoors: "They have reappeared in the human psyche. It is significant that in their new home not even the occult ones are altogether taboo. Apart from a certain number of hard-boiled empiricists and behaviorists, most people today concede to the psyche that 'inwardness' which they deny to nature, and they call it the unconscious mind--or the unconscious" (RM 182).
See in particular "Science and Quality" (RM 176-86); Worlds Apart, passim.
1The distinction can be formulated as the difference "between the qualities possessed by things, and qualities produced in us by things. The primary qualities of things are solidity, extension, figure, motion, rest, and number. The secondary qualities are colors, sounds, tastes, smells, etc" (DPR 471).
2"In the history of the theory of color," Barfield explains in Saving the Appearances, "color began by being regarded as a primary quality of the colored object and was later transferred to the status of a 'secondary' quality dependent on the beholder" (25-26).