People who can't picture anything are rewriting the science of imagination

I think, however, that your reasoning is backwards. Language such as "picture this," "envision yourself on a beach," the concept of the "mind's eye," or especially the word "imagination" from "image" is much more likely to exist as a result of the actual process than to be its cause. Parsimony favors assuming that the description evolved from the experience - if nobody "saw" mental imagery, we would more readily describe the thought process as "thinking about," "reasoning around," that sort of thing.

The language used cannot be used as proof on its own. What makes me think this is more than a description problem is that reported vividness of imagery correlates to unconscious effects: pupils constrict to imagined bright shapes and dilate to imagined dark ones, scaled to how vivid the person says the image was[0]. People reporting aphantasia don't show those effects. Despite this not constituting "proof," I cannot rationalize it being a coincidence.

If it matters, I call myself aphantasic, though I cannot prove it to you. You may relate to my initial thought - "surely all this language is metaphor, and people don't really walk around hallucinating on command." Taking (the vast majority of) people at their word, however, indicates that they really do see things when they think about them - though visual mental imagery is meaningfully different from actually seeing (but is more like seeing than aphantasics assume). Refer to Galton's original 1880 study[1] for 150-year-old rationalizations that are the same as mine.

[0] https://elifesciences.org/articles/72484 [1] https://psychclassics.yorku.ca/Galton/imagery.htm

you can roughly draw the object from memory

you can name its main parts

you can name its main colors

you can describe its spatial orientation

The image shouldn't be as clear as a hallucination, and it should be a memory of a specific object, not a generic one. Meeting these criteria is already enough to link another image to it, for example by piercing it with another object, though there's also the question of imagining it at a large enough size.

Aphants, do these hold for you? Take Doge, the popular meme dog: not a generic Shiba Inu, but that exact picture. Could you sketch it, name its parts and colors, and say which way it's facing? And could you imagine, say, a pencil piercing it?

Telling people to imagine a cone, then a plane, then rotating the other slightly and slice through the cone without touching the base, and then looking at a normal angle at the 2D shape of the resulting intersecting surface is a really good way to explain ellipses.

IF the person you're talking to can do all these steps. Turns out some people can rotate a cow in their head and some can't. If you cannot, a drawing or animation can help a lot to get the point across. Now I haven't gotten a problem with imagination at all, but I can only imagine how hard some subjects might be if you can't do that in your head.

I just realized that I can't imagine things and visualize a picture of it! If I try to imagine an apple, I've got nothing - although of course I know what one looks like. There is just zero mental imagery if I try to imagine one.

I just asked my daughter to imagine seeing an apple with her eyes closed, and she said yes she can see it. I asked what did she see "an apple sitting on a table". Did it have a color "yes it is red". I've got none of that - not even a fuzzy round grey thing. I know what it looks like but just can't/don't conjure up an image of it.

I don't even understand exactly what my daughter is experiencing. I said I just see dark when my eyes are closed - no image of an apple. She says she of course sees dark too, but there is also some experience of seeing an apple. I asked her to visualize something with her eyes open, and she can do that too (I guess this is normal), she still visualizes it, but somehow separate from the reality she is also seeing with her eyes open.

It seems pretty clear that what I experience, and what my daughter does, when trying (or succeeding) to visualize something are very different.