An INUS theory of causal conditional reasoning

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An INUS theory of causal conditional reasoning is proposed. It builds on Mackie's (1980) analysis of causes as causally prior INUS (i.e., insufficient but non-redundant parts of unnecessary but sufficient) conditions and addresses reasoning with causal conditionals of the form "If cause A is present, then the effect B occurs." According to the INUS theory, causal conditionals are interpreted as asserting that A is a causally prior INUS condition for B implying that "AX or Y if and only if B" with complementary necessary conditions X and alternative causes Y left largely implicit and unspecified, but by default assumed to be true (X) and false or of unknown truth value (Y), respectively. The INUS theory accounts for findings from the classical (deductive) and the new (probabilistic) paradigm of conditional reasoning within a common framework. Predictions are tested regarding the classical paradigm (1), the new paradigm (2-3), and their interrelationship (4): 1) The theory predicts a rich range of different inference patterns in the classical suppression paradigm (Byrne, 1989). 2) The theory predicts that documented discrepancies from the norms of probability (e.g., the neglect of alternative causes in so-called probabilistic modus ponens; Fernbach & Erb, 2013) can be eliminated if reasoners' interpretation of the questions put to them is taken into account. 3) The theory challenges the empirically well-supported "Equation" (P(If A, then B) = P(B | A)) in the new paradigm. 4) The theory predicts new, as yet undiscovered, dissociations between the classical and the new paradigms to occur in suppression-paradigm experiments.