© koninklijke brill nv, leiden, 2020 | doi:10.1163/18756735-000098 grazer philosophische studien 98 (2021) 50–74 brill.com/gps Abduction as a Method of Inductive Metaphysics Gerhard Schurz University of Düsseldorf, Düsseldorf, Germany gerhard.schurz@phil.hhu.de Abstract Like scientific theories, metaphysical theories can and should be justified by the inference of creative abduction (sec. 1–2). Two rationality conditions are proposed that distinguish scientific from speculative abductions: achievement of unification and independent testability (sec. 3). Particularly important in science is common cause abduction (sec. 4). The justification of metaphysical realism is structurally similar to scientific abductions: external objects are justified as common causes of perceptual experiences (sec. 6). While the reliability of common cause abduction is entailed by a principle of (Markov) causality (sec. 5), the latter principle has an abductive justifica- tion based on statistical phenomena (sec. 7). Keywords inductive metaphysics – common cause abduction – causality – metaphysical realism – brain in a vat 1 Introduction: The Program of Inductive Metaphysics Two competing understandings of the method of metaphysics can be discerned: 1.) Metaphysics as an a priori discipline that explicates the essences of be- ings either by logico-semantic analysis of fundamental concepts (cf. Lowe 2011; Fine 2012) or by fundamental intuitions (Bealer 2002), but independently from experience. Historically this understanding of metaphysics roots in the ratio- nalist and the Kantian wings of enlightenment philosophy, though in rather different ways: while rationalists (e.g., Leibniz) thought that human cognition