The issue “realism vs. phenomenalism” or “realism vs. positivism” has been widely discussed during the last fifty years. The issue has even become a political and social one in Lenin's Materialism and Empiriocricism, which is built entirely around this topic. He calls “positivism” bluntly a “reactionary philosophy” because it supposedly denies the reality of the world which is described by science. M. Schlick devoted to this issue the paper “Realism and Positivism” which was published recently (in English) with an introduction by D. Rynin. It should, therefore, be welcomed, that Professor Feigl attacked this problem by the methods of modern semantics. This is an attempt to solve a question by precise logical argument which has been frequently treated in a way that provided more heat than light. It is certainly very desirable to scrutinize Feigl's argument carefully and to find out exactly its contribution to our conception of scientific method.