A common historical and intellectual connection is the Vienna Circle, which was a group that met in Vienna during the 1920s and 1930s and developed the philosophy of logical positivism, which was intent on setting philosophy on a sure footing so that the scope of its tasks was clear. Logical positivism, by way of a theory of meaning, involves the elimination of much of traditional philosophy, in particular metaphysics and also theology, as literally meaningless. Both A. J. Ayer and Karl R. Popper attended the meetings of the Vienna Circle, but whereas Ayer initially became a powerful advocate of its views, Popper, although deeply interested, like the Vienna Circle, in the philosophy and methodology of science, was critical of logical positivism. Popper aims to demarcate science from non-science so as to understand better the nature of scientific knowledge. In Popper's falsificationism, the source of a scientific theory is totally irrelevant to whether it is scientific or not.