observer and to see something more, something real, behind him and his measurement, This outlook cannot be challenged from the purely logical viewpoint. And yet, a closer exami- nation must brand this version of it as inadequate and unproductive. For it disregards a circum- stance which is of a decisive importance in the extension and progress of scientific knowledge. However much Positivism may regard itself as proceeding without presuppositions, it is nonethe- less committed to a fundamental premise if it is not to degenerate into an unintelligible solipsism, ‘This premise is that every physical measurement can be reproduced, so that its outcome depends neither on the personality of the individual per- forming the experiment, nor on the place and time of the measurement, nor on any other at- tendant circumstance. But this simply means that the factor which is decisive for the result of the measurement lies beyond the observer, and that one is therefore necessarily led to questions con- cerning real causal connections operating inde- pendently of the observer. To be sure, it must be agreed that the posi- tivistic outlook possesses a distinctive value; for