The Inherent Empirical Underdetermination of Mental Causation

ABSTRACT

It has become a popular view among non-reductive physicalists that it is possible to devise empirical tests generating evidence for the causal efficacy of the mental, whereby the exclusion worries that have haunted the position of non-reductive physicalism for decades can be dissolved once and for all. This paper aims to show that these evidentialist hopes are vain. I argue that, if the mental is taken to supervene non-reductively on the physical, there cannot exist empirical evidence for its causal efficacy. While causal structures without non-reductive supervenience relations can be conclusively identified in ideal discovery circumstances, it is impossible, in principle, to generate evidence that would favour models with mental causation over models without. Ascribing causal efficacy to the mental, for the non-reductive physicalist, is a modelling choice that must be made on the basis of metaphysical background theories or pragmatic maxims guiding the selection among empirically indistinguishable models.

KEYWORDS:

• mental causation
• causal exclusion
• causal modelling
• interventionism
• empirical underdetermination
• non-reductive physicalism

Notes

¹ Correspondingly, interventionism would not be an adequate theory of causation if the notion of an intervention were relativized to a variable set [Woodward 2008b: 201–3; Baumgartner 2013: 11–13].

² For an extended argument as to why constitution is a non-causal form of dependence, see Craver and Bechtel [2007].

³ A fat-handed intervention is an intervention that influences its effects along two (or more) different causal paths [Scheines 2005: 931–2].

⁴ To be fair, this is my reconstruction of how interventionism* resolves the empirical underdetermination of mental causation. Woodward [2015] himself does not view interventionism* as establishing mental causation by means of a definitional fiat. As he contends that mental causation models and their epiphenomenalist rivals do not represent different causal structures, he denies that there is empirical underdetermination to begin with. A consequence of this view, however, is that the ongoing debate between non-reductive physicalists and epiphenomenalists is a meaningless pseudo-debate over the truth of causal models that do not represent different structures. Plainly, this perspective likewise undermines the evidentialist project, for there is no reason to design tests that could adjudicate between positions that do not differ in the first place.

⁵ A variable $X$ screens off two variables $A$ and $B$ iff $\mathrm{P}\left(B\right|A)\ne \mathrm{P}(B)$ and $\mathrm{P}\left(B\right|X\wedge A)=\mathrm{P}(B\left|X\right)$.

⁶ I am grateful to the audiences at the workshop on Emergence, Exclusion and Causation, University of Glasgow, April 2016, and at the conference on Causality in the Sciences of the Mind and Brain, University of Aarhus, June 2016. Moreover, I thank three anonymous reviewers for their helpful comments and suggestions.

Additional information

Funding

Research for this article was supported by the Swiss National Science Foundation, grant number PP00P1_144736/1.