From Speaker's Meaning by Owen Barfield (1967) - edited from pages 71-72:
It is generally supposed that the 'public' world which we have in common with others consists entirely of what we perceive; and the private world of each person consists of what he thinks.
Yet the exact opposite is the case: It is the thought content which we share with others, while our perceptions are private to ourselves.
The above formulation (which I have condensed and slightly rephrased for clarity) shows the radical nature of Owen Barfield's philosophy - it is so much in conflict with mainstream modern thinking as to seem just plain bizarre, or crazy; yet the contention is justified across hundreds of pages of argument and evidence in Barfield's main works.
It is easy, and in a sense uncontroversial - despite being ignored in everyday life, to point-out that our perceptions of The World are private, 'subjective' - because it is recognised that everybody sees, hears and feels things differently, and that such perceptions have been manipulated and disrupted by many illusions, technologies, drugs, diseases and just from individual and cultural differences. At another level, we all know that the world described by science - especially physics - is utterly different from the world we perceive.
What is hard for modern people to grasp or believe is that we share our thought content with others.
This does not mean telepathy; it does mean that when we think, this is happening in a shared, universally-accessible realm. It is this world of thinking that unites people - and not the world of perceptions.
It is strange to modern people to suppose that there is or can be a shared world of thought - mostly we can't even imagine this. We moderns suppose that thinking is restricted to our own heads, our own brains - but for thought to be universal, then thinking must be located in some state or place that is universally accessible.
Yet in the past it was apparently taken for granted that there was a spirit world, an 'underworld' - e.g. the Ancient Egyptians' Dwat. This was not located elsewhere, but within - apparently people had no trouble in supposing that the Dwat was within everything, and also everywhere - it was a kind of unbounded space that was inside everything - and also from-which everything perceptible came, and to which it returned.
In more recent times, Jung posited a 'collective unconscious', of myths and archetypes, which shares some of these aspects and was supposed to be accessed in dreams and trance states. Yet for Barfield this world of thinking is conscious as well as unconscious.
Perhaps we can think about this, imagine it, only if we understand the world of thinking to be primary - and the perceptible world to be secondary. The world of thinking is therefore everywhere; and it is the perceptible world which is restricted and located - as it were 'within' the world of thoughts.
Everything began as thought - and the perceptible world was condensed and concentrated from it.
We actually live in the world of thinking; but have partly learned, partly developed the habit, of cutting ourselves off from it - because that is how we became free agents.
Now that the process of becoming free agents is complete - we can, and should, voluntarily and deliberately, return to engage with, participate-in, the world of thoughts - but this time with freedom, agency, and awareness of what we are doing. (In the past we just took it for granted, were unaware of it - passively lived-by-it.)
First we need to recognise that our thinking is in a universal realm - and then we may exercise our freedom within this realm of thinking - not just understanding it, but changing it.
This conscious participation in the realm of universal thinking is the ultimate in creativity - indeed, the only true creativity; because it shares in the divine.
God created what is and wished for us to share it - not merely passively, but as co-creators, to work with God and to develop and enhance creation in the loving spirit it which it was made.