A coherentist approach to probabilistic causal assessment                 

Abstract: Philosophical discussions on causal inference in medicine are stuck on dyadic camps, each defending one kind of evidence or method rather than another as best support for causal hypotheses. So, whereas Evidence Based Medicine advocates invoke the use of Randomized Controlled Trials and systematic reviews of meta-analyses as gold standard, philosophers of science emphasize the importance of mechanisms and their distinctive informational contribution to causal inference and assessment (Illari et al., Williamson and Russo 2011, Cartwright 2011, Clarke et al. 2013, Howick 2015); one of the most sophisticated tools for inferring causes from probabilistic distributions, Causal Bayesian nets, instead has been criticized for failing to take into account interacting causes, feedback phenomena and hierarchical causal structures (Casini et al. 2011, Clarke et al. 2014, Weisberg 2007). Related to this debate is also the discussion on the internal vs. external validity tradeoff in causal inference (Steel 2007). As possible solutions to these problems, scholars suggest the adoption of a pluralistic approach to causal inference, and an inductive rather than hypothetico-deductive inferential paradigm (Godfrey-Smith 2010, Cartwright 2011, Osimani 2013, 2014). However these proposals deliver no clear guidelines about how such plurality of evidence sources should jointly justify hypotheses of causal associations. In methodological writings the adoption of Bayesian or hybrid statistical methods is advocated, which would enable a probabilistic assessment of hypotheses, the incorporation of various kinds of knowledge in the prior, and hypothesis update in the face of new evidence (Price et al. 2014). Although this is a progress in practical terms, I propose a "step back" from a focus on methodology to one on epistemology and suggest that (Bayesian) coherentism is the best candidate for providing foundational groundings for probabilistic causal assessment from heterogeneous evidence. Furthermore, I advance that coherentism may well be the best investigational instrument also in a “pragmatic” perspective, by providing the right tools to model the implicit intuitions lurking in many debates on evidential support of causal hypothesis in the biomedical and social sciences, where surface methodological dissent can be traced back to differing epistemological stances. I illustrate this by means of a case study from pharmacology.