OPEN MIND

An open mind, in questions that are not ultimate, is useful.  But an open mind about ultimate foundations either of Theoretical or Practical reason is idiocy. If a man's mind is open on these things, let his mouth at least be shut. 

C.S. Lewis quoted in Credenda Agenda Vol. 4, No. 5 p. 16.

Merely having an open mind is nothing; the object of opening the mind, as of opening the mouth, is to shut it again on something solid. 

G.K. Chesterton