Logical positivism
Logical positivism was a movement in the early 20th century that tried to reduce the reasoning processes of science to pure logic. Among other things, the logical positivists claimed that any proposition that is not empirically verifiable is neither true nor false, but nonsense. This movement faded out due to various problems with their approach among which was a growing understanding that science does not work in the way that the positivists described. Another problem was that one of the favorite slogans of the movement: "any proposition that is not empirically verifiable is nonsense" was itself not empirically verifiable, and therefore, by its own terms, nonsense.