此两者同，出而异名。 同谓之玄，玄之又玄，众妙之门。 Under these two aspects,it is really the same; but as development takes place,it receives the different names. Together we call them the Mystery. Where the Mystery is the deepest is the gate of all that is subtle and wonderful. 玄：神妙难捉摸，深奥[mystic;profound;abstruse] 问题：“常有”、“常无”怎么会“同”？