I found the following inscription above a sundial outside the York Minster:
LVCEM DEMONSTRAT VMBRA
This seems extraordinarily poetic to me, for many reasons. One reason is the reversal of prosaic word order, aligning with the reversal of light's ordinary role from what shows us things to the thing being shown. Another reason is more of a guess on my part: does de- suggest a perspective of looking downward upon something—even in the word demonstro? If so, then the sentence reverses light in another way, since normally sunlight is above and shadow is below.
I've been thinking that the primary sense of de is a perspective of "from higher to lower", as in de cælo demissus, descendo, etc., and the other senses, such as "about", "all the way", and "to destruction", are extensions of the primary sense—and as often happens, the primary sense tends to linger on in the secondary senses. "About", as in the topic of a book, fits the perspective of looking down from above, where you can "see" the whole of the topic. Destruere is to send what has been built back down to the ground; devolvere is to roll downhill or delegate authority "downward"; and countless more examples. Deesse is to be away from where you're expected, suggesting that de takes a steady, upright perspective from which other things are perceived as falling down or straying. Even much later neologisms seem to retain this meaning, like "decadent", which seems to emphasize falling away from a higher state of culture. I've inferred this somewhat subconsciously from learning words and reading, not from any explicit description, though I just checked Forcellini and he seems to agree that the spatial sense is the primary one. If I'm wrong about this, please let me know.
Assuming that the spatial sense is primary, then, is it a completely dead metaphor in demonstro or does that word still convey some sense of a perspective of looking down from a higher perspective, somehow "coming down"? Are there other pithy or poetic Latin sentences whose punch derives from activating the downward spatial sense of "de" even in a word that seems to have forgotten it? Or to put this yet another way, what does demonstro have that monstro lacks?