Logical positivism (sometimes referred to as simply positivism) asserts that only statements about empirical observations are meaningful, effectively asserting that all metaphysical statements are meaningless. At one time, positivism was the dominant theory of the philosophy of science.
Some commentators have attacked logical positivism on the basis that this fundamental tenet is itself a metaphysical statement, presenting severe problems for the logical consistency of the theory. In response, positivist theorists have created a special category of 'statements about language' to deal with this problem.
Books: Ayer, A. J.; Language, Truth and Logic, ISBN 0486200108