Convention? What kind of convention is that? Agreement or compromise?

"By convention there is color, by convention there is sweetness, by convention bitterness, but in realty there are atoms and space.

—Democritus"

Convention? What kind of convention is that? Agreement or compromise?

Convention? Like interpretation? How the mind instantiates 'realty'? Or, how human minds, as a 'populace' agreed to look upon 'realty'? A second stage act following a first stage act of a single human mind observing 'realty', and after that, it passes its concluded thoughts about the observations, as it sits down with other mind-bearers to agree to a common approach. On how to interpret the conclusions amassed, provide a name-symbol, and use it to depict what is conceived? The stuff of concepts? Reaching an accord? At least that is how reason should work.

Or is it convention within a single mind, that makes the 'atoms and space' realty into something that agrees with its unit make-up, its senses and its body? And since, its senses and its body, are what it has to work with, it can not do anything else, but use them. Convention being more like a compromise? Its unit make-up, a result of endless processes between the 'atoms and space', that realty is, have confined the individual in a level of existence, isolated from all other levels above and below, trapped, bound by impenetrable boundaries? Only its mind is left out free to roam at any level, up or down, and beyond? Traverse right down to the bottom levels, even further below than 'atoms and space' lay?

The space of the DM is certainly not the space of the RUCA.

Why is the mind capable to traverse impenetrable boundaries? Is it because what lies down there, is made out of the stuff, the mind is made up from?