Combining Pluralism and Scientific realism (in quantum physics): Putnam’s Pragmatic Realism

In this presentation, I explore the possibility of combining pluralism and scientific realism in the framework of Putnam’s pragmatic realism (Putnam, 1999; Bernstein, 2005). I illustrate my claim through the analysis of a case of Duhem-Quine underdetermination originating in the violation of Bell’s Inequalities and involving several contemporary conceptions of quantum mechanics: the instrumentalist approach called ‘no interpretation view’ (Fuchs and Peres, 2000), Bohmian Mechanics (Dürr and Teufel, 2009), the veiled reality conception (d'Espagnat, 2011) and the approach with extended probabilities (Gell-Mann and Hartle, 2012). First, I briefly expose how the violation of Bell’s Inequalities can be understood as imposing a necessary trade-off between epistemic values usually satisfied in the context of classical physics. This allows conceiving the proponents of the studied approaches as standing in “faultless” or “rational” disagreement (Gattei, 2008; Pritchard, 2009). However, while the idea of faultless disagreement becomes more and more accepted, pluralism is rarely advocated for beyond the epistemological (cognitive) human sphere. Indeed, while it is often acknowledged that several competing theories can all be reasonably endorsed (Kelly, 2005), admitting that more than one is really is usually considered as opening the door to anti-realism (about entities described by scientific theories and about truth) or to relativism. I then mobilize Putnam’s pragmatic realism to challenge this last claim, in discussing the possibility of admitting a plurality of true theories while preserving scientific realism and realism about truth. The core of Putnam’s conception is to reject sense data (or inner theater) epistemology in considering that genuine aspects of reality (and not mere mental phenomena) are met in our ordinary perception (Putnam, 1999, 2013). Putnam arrived at this conclusion after a long intellectual path initiated with the rejection of metaphysical realism and its associated understanding of truth as a unique (and transcontextual) substantive property (of correspondence to the metaphysical reality). Putnam first opposed to this type of view his internal realism in which truth becomes intimately connected to standards of rational acceptability, opening the road for conceptual pluralism (Putnam, 1981). However, this first attempt proved unsatisfying, providing no sufficient ground for realism and for discrimination between truth and verification. Putnam diagnosis is then radical: in the framework of sense data epistemology, one cannot escape the forced choice between metaphysical realism and verificationism – this is the antinomy of realism (Putnam, 1999). With pragmatic realism and the rejection of the inner theater picture, Putnam proposes an interesting alternative. It becomes possible to admit the disquotational conception of truth from Tarski while 1) escaping its deflationist interpretation without returning to metaphysical realism and 2) maintaining conceptual pluralism. According to pragmatic realism, the way a knowledge claim can be responsible to reality – can be true – is neither unique nor fixed in advance. As it will be illustrated with the discussion of the disagreement about quantum mechanics, this pragmatic realism framework permits the combined admission of conceptual pluralism and scientific realism. • Bernstein, R. J. (2005). In Y. Ben-Menahem (Ed.), Hilary Putnam (pp. 251-265): Cambridge University Press. • D'Espagnat, B. (2011). Foundations of Physics, 41(11), 1703-1716. • Dürr, D. and Teufel, S. (2009). Bohmian Mechanics: Springer Berlin Heidelberg. • Fuchs, C. A. and Peres, A. (2000). Physics Today, 53(3), 70-71. • Gattei, S. (2008). Thomas Kuhn's "Linguistic Turn" and the Legacy of Logical Empiricism: Incommensurability, Rationality and the Search for Truth: Ashgate. • Gell-Mann, M. and Hartle, J. B. (2012). Physical Review A, 85(6), 062120. • Kelly, T. (2005). In T. Szabó Gendler and J. Hawthorne