People often talk as if nothing were easier than for two naked minds to “meet” or become aware of each other. But I see no possibility of their doing so except in a common medium which forms their “external world” or environment. Even our vague attempt to imagine such a meeting between disembodied spirits usually slips in surreptitiously the idea of, at least, a common space and common time, to give the co- in co-existence a meaning: and space and time are already an environment. But more than this is required. If your thoughts and passions were directly present to me, like my own, without any mark of externality or otherness, how should I distinguish them from mine? And what thoughts or passions could we begin to have without objects to think and feel about? Nay, could I even begin to have the conception of “external” and “other” unless I had experience of an “external world”?
— C.S. Lewis, The Problem of Pain