It is time to take stock. We began with three commonplace theses about mental phenomena and their physical realization in the brain that together generate a profound puzzle about mental causation. This is the content causation problem: that of explaining how the specifically representational properties of mental phenomena can be causally efficacious of behaviour. This problem has an air of insolubility about it because it appears to require something impossible: an explanation of the relational character of mental content that invokes only the intrinsic properties of the brain. It has been the foundational conjecture of this discussion, however, that this despair issues from the impoverished understanding of content that attends the dyadic analysis of mental representation, and that once we adopt the perspective of the triadic conception our view of the content causation problem is transformed.
The insight offered by triadicity is that the relational character of mental content is to be discharged ultimately in terms of our behavioural dispositions towards features of the world. This offers a way forward with the content causation problem because it suggests that, rather than seeking to explain some kind of mysterious action-at-a-distance, the task for a theory of content determination is to explain how the obtaining of world-mind relations can dispose cognitive systems to respond selectively to certain elements of their embedding environments.
According to most naturalistically-inclined philosophers, there are just two candidate mind–world relations available: causal relations and resemblance relations. Causal theories of content determination dominate the contemporary landscape, but our analysis confirms what many have suspected—namely, that causal theories offer no prospect of a solution to the content causation problem. The reason for this, however, is not because such theories appeal to relations that incorporate factors beyond the brain. All theories of mental representation, in their efforts to explain the relational character of mental content, are forced to invoke world–mind relations of some kind. The problem with causal theories, at least from the triadic perspective, is the disconnect between world–mind causal relations and a system’s behavioural dispositions. The obtaining of causal relations between external conditions and inner vehicles cannot explain how the latter endow systems with the capacity to respond in a discriminating fashion towards the former.
This leaves us with resemblance relations. The problem here is that resemblance theories of content determination have for many years been deeply unpopular in philosophy. But this is another point where the triadic conception of representation pays rich dividends. Most of the problems associated with resemblance theories don’t look so severe when viewed from the triadic perspective. This is encouraging, because resemblance does offer some prospect of a solution to the content causation problem. The key here is that the mere obtaining of the resemblance relation entails that representing vehicles replicate their represented objects. This ensures that the former have properties that can be exploited to shape the behavioural dispositions of cognitive systems towards the latter.
Consequently, if the line of argument presented here is on the right track, then resemblance theories of mental content determination must be rehabilitated and subjected to scrutiny and development. It goes without saying that there are a great number of significant hurdles yet to be overcome. I have focused, for instance, on just one very simple example of a representation-using system. There remains, accordingly, a large question mark over whether the resemblance solution to the problem of content causation scales up to more sophisticated cognitive creatures, let alone to the immense complexities of our own mental phenomena. But we have to start somewhere. And as things currently stand, resemblance theories appear to be obligatory, since they alone offer some prospect for explaining how mind matters.