Tropes, Mental Causation, and the Problem of Causal Exclusion

Douglas Ehring has argued that one can avoid the Problem of Causal Exclusion if one adopts a trope theory of mental properties within the context of part-whole physicalism. Ehring attempts to show that the reasoning behind the Problem of Causal Exclusion is invalid. His argument characterizes the Problem of Causal Exclusion as an argument chiefly about overdetermination. Ehring then argues that a trope theory of mental properties can escape the Problem of Causal Exclusion because it avoids the type of problematic overdetermination that the Problem of Causal Exclusion rejects. In this paper I will show why Ehring's response to the Problem of Causal Exclusion is inadequate to show that Causal Exclusionary Reasoning is invalid.

Ehring adopts a trope theory of mental and physical properties. On a trope theory, particular instances of mental and physical properties are not instantiations of generalized properties. These particular instances are rather individualized spatiotemporal particulars. Because tropes are defined in terms of particulars, each trope is unique in its being defined by all the particular facts that differentiate that trope from any other. Since each trope is so heavily laden with particular facts of differing sorts, trope theory accommodates the view that a single trope can be a member of multiple types of tropes, on the view that types are merely sets of sufficiently similar tropes. Ehring argues that particular tropes can be members of both mental and physical trope types, and that this sort of local trope identity eliminates the necessity of overdetermination of physical effects by more than one type.

According to Ehring the Problem of Causal Exclusion is a problem about overdetermination. Since particular mental states and physical states, on Jaegwon Kim's view, are instantiations of universally generalized mental and physical properties, the competition between mental and physical causes on Kim's view is a competition between differing mutually exclusive property types. Since according to non-reductive physicalism, mental properties and physical properties are non-overlapping, distinct types, the two types will create an overdetermination problem when relating mental properties and physical properties to a specific causal effect. But it is the mutual exclusivity of mental and physical properties or types that creates the problem of overdetermination behind the Problem of Causal Exclusion for Ehring.

Ehring's solution to this problem is to argue that a single trope can be of more than one type, since types are merely sets of similar tropes with individual tropes as members of the sets. Since a spatiotemporal particular may have a number of distinct properties (not in the metaphysical sense), a single trope may be a member of more than one type based on similarities between aspects of the trope in question and other tropes with similar aspects. Ehring argues that it is not inconsistent therefore to claim that a single particular trope may be a member of both a mental type and a physical type, where those types are merely aggregates of individual tropes with particularized characteristics.

Ehring argues that mental types may plausibly be assumed to be multiply realizable. This multiple realizability allows Ehring to claim that Mental and Physical types are non-identical and causally relevant without the unhappy result that mental and physical types present a problematic form of overdetermination. Ehring argues that mental types, which again are simply sets of tropes, are composed of physical types, which themselves are aggregates of species-specific physical tropes. Ehring thus uses the local identity of mental and physical tropes to argue that the same causally relevant trope can be a member of both a mental and a physical type but that the types themselves do overdetermine the resulting effects. An individual physical trope is aggregated together with sufficiently similar tropes into species-specific physical sub-types, which are sets of these individual tropes. According to the supposition of multiple realizability, this physical sub-type will be merely one way in which a mental type could be realized. A mental type, then, will consist of the individual physical tropes from one species-specific physical sub-type along with the physical tropes from any other species-specific physical sub-types that may also be realizers of the same mental type. This means that one and the same trope can be members of both a physical type class and a mental type class without the types themselves being identical to one another. This reasoning is supposed to show that the Supervenience Argument is invalid insofar as it undermines the move Kim makes toward epiphenomenalism to avoid systematic overdetermination by competing property types. Ehring also offers reasons to think that a trope within a class can have causal relevance without the class as a whole having causal relevance, which diffuses the causal tension between competing types of tropes.

The move to trope theory from a theory of universal properties immediately carries a burden to explain why such highly localized and particularized tropes are naturally arranged into types instead of arbitrary sets. Ehring fails to give an adequate account of why certain tropes naturally fall into the same category, often stating that the individual tropes must be sufficiently similar, but this is unhelpful as an account of what that similarity resides in. So an initial objection that could be raised against a trope approach to mental causation is that one cannot account for the similarity of tropes without appealing to a more general quality, such as a universal property. It is possible that a functionalist approach could be used to attempt to explain this natural similarity, but there is the same problem in grouping analogous functional relationships together in sufficiently similar groupings rather than arbitrary sets. One might worry that by appealing to similarity in one's account of trope theory, especially in light of the way in which Ehring's argument is dependent upon similarity to make the case for non-overdetermination due to multiple realizability by different physical sub-types (which are based in similarity), that trope theory is not able to maintain a sufficiently different account of the nature of the mental and the physical without smuggling in the notion of an abstract property. And if one must ultimately appeal to an abstract property to account for similarity, then an account of how a single trope could fall into more than one non-competing type would be in jeopardy.

A second objection that could be raised against Ehring's trope account of mental causation is a worry that he has misrepresented the problem about overdetermination in such a way as to make the problem easier to solve with trope theory. Ehring makes a distinction between local/trope identity and identity of types. By dismissing local identity as unproblematic for mental causation and by diffusing the worry about overdetermination by types, Ehring claims to have a solution to the Problem of Causal Exclusion that avoids the epiphenomenalism that could follow from Causal Exclusionary reasoning. However, one of the distinguishing characteristics of Jaegwon Kim's Supervenience Argument is that Kim attempts to remain absolutely neutral about the nature of mental properties and physical properties. Regardless of what the m and p in his diagrams are interpreted to be, one can run through the reasoning in the Supervenience argument and be forced in the direction of a discussion on overdetermination. And if one does opt to take the route of local identity, as Ehring does, then one might still ask about the causal status of m and p with respect not only to physical effects in general but to novel effects. Surely if m and p (whether tropes or properties) are identical, then if p is causally efficacious then so is m. But it seems to me that one could still ask whether m is a necessary postulation given that physical effects are necessitated sufficiently by their causes in virtue of their physical properties. One could reply, as Ehring does, that one and the same particularized trope could be both mental and physical, and since the physical trope is a cause, the mental trope is also ipso facto a cause of the effect. I see two worries with this response. One worry is that part of the motivation for retaining a robust account of mental causation is to allow one to retain a sense of voluntary action. Voluntary action seems to me dependent upon the view that mental properties introduce novel effects into the physical domain. So if Ehring's trope theory does not allow for novel effects, then it does not grasp the point of the desire to retain a robust theory of mental causation. The second worry is that Ehring's trope theory, by equating mental and physical tropes essentially makes each instance of a causal trope only causally efficacious in virtue of its being in the physical type set and not in the mental type set. While it is true that one and the same trope may be both, on Ehring's account, it seems to me that one must still appeal to the difference in similarity between physical tropes and mental tropes to explain why any given trope is able to bring about a physical effect. In other words, if a trope is causally efficacious in the physical domain, then it is because the trope falls into the type/class of physical tropes. Why does a trope fall into that class? Because they are similar. Why are they similar? The answer to this question seems to me to violate Ehring's restriction against appealing to abstract properties. At worst, if only physical tropes can bring about physical effects, it seems that those tropes that also happen to be mental tropes are not causally efficacious in virtue of their being mental but just in virtue of their being physical. So again we are left with a puzzle that is similar to that offered by Jaegwon Kim in his Supervenience Argument. Rather than m and p standing for universal properties, it seems to me that we could interpret Kim's diagrams in light of the similarities between tropes. P could stand for whatever it is about a trope that makes it naturally fall into a physical type/set, and m could stand for whatever it is about a (single) trope that makes it naturally fall into a mental type/set. Since the physical characteristics of a trope are adequate to provide a sufficient causal explanation of resulting physical effects, it seems that we can still follow Kim in saying that the mental could only be causally efficacious in virtue of its being necessarily attached to the physical, and that in fact it is the physical characteristic (resisting the term "property" to grant Ehring as much of his terminology and assumptions as possible) of a trope that does the causal work.