CONGRUENCE The aim of this lecture is to establish a theory of congruence.

You must understand at once that congruence is a controversial question.

It is the theory of measurement in space and in time.

The question seems simple.

In fact it is simple enough for a standard procedure to have been settled by act of parliament; and devotion to metaphysical subtleties is almost the only crime which has never been imputed to any English parliament.