Haller's writings on aesthetics and the philosophy of art are less well known than his work on the history of Austrian philosophy, on Wittgenstein, and on issues in the philosophy of science and epistemology. Haller himself seldom refers to them. But there is a telling passage in the preface to his volume Facta und Ficta where he says that the contrast expressed by this title, the contrast of factual and fictitious objects, is a mirror in which he sees himself, can recognize himself. "It reflects", he writes, "the wavering between various positions of empiricism and the recurrent devoting of oneself to the world of art." In it, also, the scintillating character of our ability to pursue scientific research reveals itself: the austerity of rational thinking on the one hand, and poetic fantasy on the other, the "unlimited freedom of supposing, positing and feigning possible and impossible objects and states of affairs".¹ Indeed Haller's arguments on art and on aesthetics turn out to be the hidden link, the connecting element, between the fundamental, sometimes apparently diverging, positions he holds in other domains of philosophy.