Putnam's progress: Quantum theory and the flight from realism

Mathieu Guillermin

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

G. C. Ghirardi

Christopher Norris

In this essay, I offer a critical evaluation of Hilary Putnam's writings on epistemology and philosophy of science, in particular his engagement with interpretative problems in quantum mechanics. I trace the development of his thinking from the late 1960s when he adopted a strong causal-realist position on issues of meaning, reference, and truth, via the "internal realist" approach of his middle-period writings, to the various forms of pragmatist, naturalized, or "commonsense" epistemology proposed in his latest books. My contention is that Putnam's retreat from a full-fledged realist outlook has been prompted in large part by his belief that it cannot possibly be reconciled with the implications of quantum mechanics for our understanding of processes and events in the subatomic domain. However, I suggest, this response should be seen as premature given the range of as-yet unresolved problems with quantum mechanics on the orthodox (Copenhagen) interpretation and also the existence of an alternative account - David Bohm's hidden-variables theory - which perfectly matches the established predictive-observational results while providing a credible realist ontology. I also examine Putnam's case for adopting a nonstandard (three-valued) "quantum logic" in relation to the thinking of other philosophers - Michael Dummett among them - who have espoused a more global or doctrinaire version of anti-realism. I conclude that Putnam's early (causal-realist) position is by no means untenable in light of the various arguments that he now takes as counting decisively against it.

Christopher Norris

Sanjit Chakraborty, Sudip Bhattacharyya

ABSTRACT The paper aims to bridge the history of quantum theory with its philosophical implications. The focus is not only on the scientific underpinnings of quantum mechanics (these theories emerged as ‘ad hoc’ responses to experimental anomalies) but also on the philosophical ramifications of its probabilistic nature and indeterminacy, which differ from classical realism. The paper examines Dirac's, Bell's, and modern views, focusing on how quantum mechanics (QM) challenges traditional notions of causality, objectivity, and truth while embracing epistemological and metaphysical perspectives. Debates over collapse theories and hidden variables are discussed, as well as Putnam's philosophical outlook, which includes his trenchant involvement with realism, logic, and the measurement problem. Finally, the paper proposes that QM represents a philosophical revolution that renews our understanding of reality, knowledge, and scientific explanation, rather than simply serving as a physical theory for assessing the prospects of quantum philosophy by connecting it to broader aspects such as relativity, causality, and scientific realism.