Guh, I am so behind on catching up with posts. (For which I have to thank ‘work’ work and the usual Christmas season weekend busy-ness. But of course I would rather have those than not to have them! )
I won’t try to catch up per se, so here is just:
Then there is the variety of appearances which might mislead without correction: if I am returning from the Moon to the Earth, I could possibly see the Sun and Earth together at the same time, and simultaneously I would be ‘looking through’ the 90+ million miles of space between them. But taken by itself, this image could be extremely misleading. The space certainly would not look like it is 90 million miles wide (because I would be looking along the space between the Sun and Earth, thus perceiving a foreshortened line, rather than perceiving the line in ‘all its length’); the Earth would look much larger than the Sun; and the Sun would have hardly any visible detail, but would be a mere pinprick instead.
(Footnote: Alternately, you yourself can go outside roughly once a month and see the full moon and the sun in the sky at the same time. Going strictly by that sensory image–especially during a solar eclipse–you might conclude they were roughly the same size; which is what many ancients did quite reasonably conclude!)
Even in the more complete sense, then, Lewis’ dictum stands: we cannot receive a fully accurate sensory impression of the relationship between things that even can be ‘seen’ (much less what cannot be seen).
And this applies to everything in our experience. If you were reading this as a physical printed and bound book, that book would right now present one appearance to you; but set it on the table, and it would present another appearance. The information you thus receive may be complementary by inference and conflation; but the mere presentations they make to your senses are not (taken by themselves) compatible, and may even be mutually exclusive.
If I throw a book at your face, its appearance shall change once again rather drastically (a blur and a bright light in sequence) and shall be accompanied by different sensory impressions (a ‘whiff’ and a burst of pain-feeling, perhaps). Even when the book sits on the table without being moved around, its appearance taken by itself is misleading to the reality of the book: it does not really have three sides (the ones visible to you at any time), but six (not counting various levels of ‘bumpiness’!)
And it is not sitting motionless on the desk. Its composite parts are in constant motion, and the book itself as a unit is hurtling through space away from the center of the universe, orbiting other galaxy clusters as part of a supercluster, orbiting other galaxies as part of a cluster, orbiting a galactic center, orbiting a star, revolving with the skin of the planet, tilting slightly as our planet’s axis shifts, and drifting with our continent on a sea of magma. All these events are happening; but we cannot detect them all simultaneously and fully, nor even keep them all properly in our minds as abstract concepts!