With this theory nature at an instant in space is an independent fact.

Thus we have to look for our preeminent congruence relation amid nature in instantaneous space; and Poincare is undoubtedly right in saying that nature on this hypothesis gives us no help in finding it.
On the other hand Russell is in an equally strong position when he asserts that, as a fact of observation, we do find it, and what is more agree in finding the same congruence relation.

On this basis it is one of the most extraordinary facts of human experience that all mankind without any assignable reason should agree in fixing attention on just one congruence relation amid the indefinite number of indistinguishable competitors for notice.

One would have expected disagreement on this fundamental choice to have divided nations and to have rent families.
But the difficulty was not even discovered till the close of the nineteenth century by a few mathematical philosophers and philosophic mathematicians.

The case is not like that of our agreement on some fundamental fact of nature such as the three dimensions of space.