The criterion which we use to test the genuineness of apparent statements of fact is the criterion of verifiability.We say that a sentence isfactually significant to any given person, if, and only if, he knows how to 44 verify the proposition which it purports to express ö that is, if he knows what observations would lead him, under certain conditions, to accept the proposition as being true, or reject it as being false.

-Ayer, SirAlfred Jules
  Language, Truth and Logic, ch.1

The only infallible criterion of wisdom to vulgar judgementsösuccess.

-Burke, Edmund
Letter to a Member of the National  Assembly.

The point of equilibrium will be known by the criterion that an infinitely small amount of commodity exchanged in addition, at the same rate, will bring neither gain nor loss of utility.

-Jevons,William Stanley
The Theory of Political Economy.