Gustav Bergmann (1906-1987) was, arguably, the greatest ontologist of the twentieth century in pursuing the fundamental questions of first philosophy as deeply as any philosopher of any time. In 2006 and 2007, international conferences devoted solely to Bergmann s work were held at the University of Iowa in the USA, Universite de Provence in France, and Universita degli Studi Roma Tre in Italy. The papers in this volume were presented at the first of these conferences, in Iowa City, where Bergmann taught for nearly four decades after escaping from Europe, following the dissolution of the Vienna Circle of which he had been the youngest member. There are nine philosophical papers, reminiscences of three of his students, and a complete bibliography of his published writings."

This volume is about ontological categories. The categories of an ontology are designed to classify all existents. They are crucial and characterize an ontology.

The two eminent metaphysicians Armstrong and Grossmann exchanged letters for ten years in which they discussed crucial points of their respective ontologies. They have a common basis. Both do metaphysics proper and not linguistic philosophy. Both advocate universals and acknowledge the key position of the category of states of affairs. However, they differ on the simplicity of universals and the nature of states of affairs. There is also a fundamental methodological disagreement between them. Armstrong accepts only the evidence of natural science and has a materialist view on mind while Grossmann is a dualist and grants also the same evidential status to the phenomenological data of perception and introspection. The letters are grouped into three phases. The first is the issue of universals, the second the ontological analysis of laws of nature and the third the ontology of numbers. The book contains also longer comments and reviews, partly not published until now.

Herbert Hochberg is one of the most influential analytical philosophers and one of the most influential critics of analytical philosophy. He disputed with almost all leading analytical philosophers, from Quine, Goodman and Wilfrid Sellars to David Lewis and David Armstrong. His point of view is ontological and he harks back to the origins of analytical philosophy where he finds unknown precursors of current views. And he finds parallels to contemporary non-analytic philosophies. In his own ontology he tries to dispense with simple particulars.