We may limit ourselves to the spaces of the parallel moments of one time-system.

How are positions in these various spaces to be compared?
In other words, What do we mean by motion?
It is the fundamental question to be asked of any theory of relative space, and like many other fundamental questions it is apt to be left unanswered.

It is not an answer to reply, that we all know what we mean by motion.

Of course we do, so far as sense-awareness is concerned.

I am asking that your theory of space should provide nature with something to be observed.