radtea wrote:Of course days of the week "exist", and have precisely the same ontological status as every other entity: they are demarcated from otherwise uncategorized reality by an act of selective attention by a knowing subject, just as the movements of the Sun, Earth and Moon are
Again I must point out that by your argument here the movement of the sun doesn't exist, as few people are regularly made aware of the motion of the sun.
You don't need to be regularly aware of something to grasp and support it as a concept.
That said, I think the whole discussion is based on semantics. Using one definition of the word real, we can argue that imaginary things are real, which might seem like a paradox. Let's take Middle-earth as an example--it's a figment of Tolkien's imagination. But Tolkien talked to us about it, and we can talk to each other about it, and we all know what Middle-earth is and what characteristics it has. Middle-earth is very real, in that sense; it influences our thoughts and behavior.
On the other hand, Middle-earth is not objectively
real or tangible. We can not touch Middle-earth, and for people who have never heard of Middle-earth, the term has no meaning if I say something about it. This is different from the Sun: we can all observe the Sun directly, and though we might disagree on its characteristics at times, to deny the existence of the Sun can't take away the sensory effects it causes.
Tl;dr, there's a difference between tangible objects and ideas or concepts, but either can be called real, depending on what definition of the word you use.