In English-speaking countries Victor Kraft is known principally for his account of the Vienna Circle. ! That group of thinkers has exercised in recent decades a significant influence not only on the philosophy of the western world, but also, at least indirectly, on that of the East, where there is now taking place a slow but clearly irresistible erosion of dogmatic Marxism by ways of think ing derived from a modem scientific conception of the world. Kraft's work as historian of the Vienna Circle has led to his being classed, without further qua1ification, as a neo-positivist philosopher. It is, however, only partially correct to count him as such. To be sure, he belonged to the group named, he took part in its meetings, and he drew from it suggestions central to his own work; but he did not belong to the hard core of the Circle and was a con scious opponent of certain radical tendencies espoused, at least from time to time, by some of its members. Evidence of this is provided by the theory of value now presented in English translation, since no less a thinker than Rudolf Carnap had, originally at any rate, obeyed a very narrowly conceived criterion of sense and declared value judgements to be senseless.

In English-speaking countries Victor Kraft is known principally for his account of the Vienna Circle. ! That group of thinkers has exercised in recent decades a significant influence not only on the philosophy of the western world, but also, at least indirectly, on that of the East, where there is now taking place a slow but clearly irresistible erosion of dogmatic Marxism by ways of think ing derived from a modem scientific conception of the world. Kraft's work as historian of the Vienna Circle has led to his being classed, without further qua1ification, as a neo-positivist philosopher. It is, however, only partially correct to count him as such. To be sure, he belonged to the group named, he took part in its meetings, and he drew from it suggestions central to his own work; but he did not belong to the hard core of the Circle and was a con scious opponent of certain radical tendencies espoused, at least from time to time, by some of its members. Evidence of this is provided by the theory of value now presented in English translation, since no less a thinker than Rudolf Carnap had, originally at any rate, obeyed a very narrowly conceived criterion of sense and declared value judgements to be senseless.

These two volumes form a full portrait of Hans Reichenbach, from the school boy and university student to the maturing and creative scholar, who was as well an immensely devoted teacher and a gifted popular writer and speaker on science and philosophy. We selected the articles for several reasons. Many of them have not pre viously been available in English; many are out of print, either in English or in German; some, especially the early ones, have been little known, and deal with subject-matters other than philosophy of science. The genesis and evolu tion of Reichenbach's ideas appeared to be of deep interest, and so we in cluded papers from four decades, despite occasional redundancy. We were, for example, pleased to include his extensive review article from the encyclo pedic Handbuch der Physik of 1929 on 'The Aims and Methods of Physical Knowledge', written at a time of creative collaboration between Reichenbach's Berlin group and the Vienna Circle of Schlick and Carnap. Reichenbach was a pioneer, opening new pathways to the solution of age-old problems in many fields: space, time, causality, induction and probability - philosophical analysis and interpretation of classical physics, relativity and quantum physics - logic, language, ethics, scientific explanation and methodology, critical appreciation and reconstruction of past metaphysical thinkers and scientists from Plato to Leibniz and Kant. Indeed, his own philosophical journey was initiated by his passage from Kant to anti-Kant."

These two volumes form a full portrait of Hans Reichenbach, from the school boy and university student to the maturing and creative scholar, who was as well an immensely devoted teacher and a gifted popular writer and speaker on science and philosophy. We selected the articles for several reasons. Many of them have not pre viously been available in English; many are out of print, either in English or in German; some, especially the early ones, have been little known, and deal with subject-matters other than philosophy of science. The genesis and evolu tion of Reichenbach's ideas appeared to be of deep interest, and so we in cluded papers from four decades, despite occasional redundancy. We were, for example, pleased to include his extensive review article from the encyclo pedic Handbuch der Physik of 1929 on 'The Aims and Methods of Physical Knowledge', written at a time of creative collaboration between Reichenbach's Berlin group and the Vienna Circle of Schlick and Carnap. Reichenbach was a pioneer, opening new pathways to the solution of age-old problems in many fields: space, time, causality, induction and probability - philosophical analysis and interpretation of classical physics, relativity and quantum physics - logic, language, ethics, scientific explanation and methodology, critical appreciation and reconstruction of past metaphysical thinkers and scientists from Plato to Leibniz and Kant. Indeed, his own philosophical journey was initiated by his passage from Kant to anti-Kant."