[js1138]

There are lots of imaginary concepts, including circles, squares, planes, pigs with wings, etc. But behind them is experience.

Next, I assume you will produce a sketch or a description of something that has no "real" parts. But it will be composed of abstractions of things experienced.

I suspect that rebellion against this was at least partly the motivation for folks like Jackson Pollack, who tried to form images with no relation to objects. This is what's known as a futile gesture. Unique objects are still objects.

[AndrewC]

There are lots of imaginary concepts

All concepts are imaginary as they are formed in the mind.

Next, I assume you will produce a sketch or a description of something that has no "real" parts.

Your wish is my command.