I wish a had a better recall with time. I can't remember how long ago it was that I found myself explaining to my class what a prism does. And, surely, I can't remember how that subject even came up. But, I do remember what I told them. Thank God for small miracles.
It was very simple to say "It's this pyramid-shaped glass thing that takes the white light and makes colors out of it." Why complicate things? The important part is that they got the idea. Something that is commonplace, ordinary and whole can be separated into many beautiful colors. All you need is a piece of glass to aim it through.
Inevitably, someone asked an unforeseen question. "Can you shine a rainbow through the prism and get the white light on the other side?" What could I say except the truth? "I've never tried." And, a few seconds later, I added, "Besides, of what use would that be?"
Pragmatically speaking, it wouldn't be useful at all. Plain light is in great abundance while rainbows are rare. There is not much sense in taking rarities and turning them into everyday things. It's like doing reverse alchemy. Making lead out of gold.
I wish I had better recall with all things. Being pragmatic implies knowing something about pragmatism. As I remember, the pragmatic maxim alludes to the notion that our conception of the effects of something is the whole of our conception of that something. Then, my conception of the prism is my conception of the effects it has on me.
What interests me here is my mind's ability to conceive of both the object and its effects. Since nearly everything is known in relation to other things, my mind can only form concepts based on the information and experiences that it has already acquired. Which is what is loosely known as "intellect." My intellect is sadly finite. The Universe, at least according to Stephen Hawking, is infinite. There really is no chance for me to conceive of any object with complete accuracy.
Is it possible that the prism integrates the many colors of the rainbow as the white light? Then, it is only my perception that it's the other way around.