The central ideas of logical, or scientific, empiricism as it developed during the twenties and early thirties in Vienna and in Berlin, grew out of collaborative efforts of scientifically interested philosophers and philosophically interested scientists. Those thinkers noted that while the claims made by the physical sciences were amenable to objective test by experiment and observation, the pronouncements put forward by metaphysics were incapable of any such objective critical appraisal. And while hypotheses advanced in the physical sciences would eventually be accepted or rejected and thus lead to the growth of a body of objective scientific knowledge, the problems and pronouncements of metaphysics, inaccessible to objective appraisal, kept reappearing over and over again.