In my attempt to follow Kant in his Critique of Pure Reason, I thought of a physics analogy to help make sense of a passage. I suppose this isn’t so off-topic since Kant is talking about metaphysics. On the need of the permanent for relations in time, Kant writes,
All relations of time are therefore possible only in the permanent (simultaneity and succession being the only relations in time); so that the permanent is the substratum of the empirical representation of time itself, and in it alone all determination of time is possible. Permanence expresses time in general as the constant correlate of all existence of appearances, of all change and concomitance. For change does not affect time itself, but only appearances in time […] (208).
The point being that there must be another vantage point outside of time for observation of change to be possible. My analogy comes about because this passage reminds me of a physics example in which someone is placed in a kind of windowless elevator in space, outside of the gravitational pull of planets. The force of gravity on earth is mass multiplied by the acceleration of earth’s gravity (9.8 meters/sec/sec). On a stable platform, this force can be felt pushing back up at us as the normal force. This upward force is equal to the gravitational force we exert upon the platform. In the space elevator, if the elevator were accelerating upward (in relation to the passenger’s sense of upward) at earth’s gravitational acceleration (or any positive gravitational acceleration), then the passenger would be unable to tell if the elevator were standing still on Earth or accelerating in space. If the elevator had windows, however, the passenger could possibly see stars, debris, etc. outside from which she could tell if she were seeing a parallax view of space as the elevator moved.