Golden rule

It is all-important to remember that naturalists have no golden rule by which to distinguish species and varieties; […]

There is one golden rule of timetable work, that if a passenger train never runs to time it must be altered or other trains must be altered so that it can shake off its chronic unpunctuality.

Here's what we call our golden rule / Have faith in you and the things you do

A new book called When Nothing Works shows which groups have enjoyed the biggest rise in take-home pay since the turn of the millennium. From Tony Blair to Boris Johnson, the authors discover one golden rule: the richer you are, the more money you’re given.

"Mr. Francis seems to understand the fundamental principle of all moral accounting, the great ethic rule of three. Let A do to B, as he would have B do to him; the product will give the rule of conduct required." My father smiled at this reduction of the golden rule to arithmetical form.