The relationship between mind and body can be described with a set of three principles (Davidson 1970, p. 116): First, the Principle of Causal Interaction. It states that at least some mental events interact causally with physical events. That means that a physical event can cause a mental event and vice versa. Examples: taking an aspirin soothes a headache. Prolongated stress might impact a person’s body. Second, the Principle of the Nomological Character of Causality. It asserts that where there is causality there must be a law that governs the relationship between cause and effect. Laws of nature, for instance, determine the orbits of the planets around the Sun. Third, the Principle of the Anomalism of the Mental. It says that there are no strict deterministic laws on the basis of which mental events can be predicted and explained. Compared to physical objects, thoughts and other mental phenomena seem to be of a different kind. They do not exhibit the sort of uniformity that can be observed in the world of physics. There is no stable relationship between one thought and another.
In isolation each of the aforementioned three principles appears to be true. However, in combination they appear to be inconsistent. How can it possibly be that mental events causally interact with the physical world? How can a thought move an atom? If the first and the second principles are true then the third must be false. If the first and the third are true then the second must be false, and so forth. Hence, the set of principles form an ‘inconsistent triad’. To remove the inconsistency, one must either identify at least one of the principles as false or find a way to show that the appearance of contradiction is misleading. The question is how.
The American philosopher David Davidson (1917 – 2003) devised a logic to resolve the inconsistent triad. He makes an important distinction between event types and event tokens. Simply put, a type is a general and abstract sort of thing while a token is a particular concrete instance of it. Wetzel cites the example of “Rose is a rose is a rose is a rose” (2014, chapter 1.1). In this sentence, there are three different types of words and ten different word tokens. Having breakfast in the morning is a type of event. Sara having breakfast with her friends earlier this morning in her favourite restaurant is a token event. It is dated, individual and unrepeatable. Because that very event can happen only once it cannot be said to be correlated with another event. For correlation to emerge there needs to be repetition and that is, by definition, not possible for token events. Only types of events can exhibit correlations some of which seem to follow laws of nature. An example from the world of physics: on sea level, water always starts to boil when heated up to 100 degrees. This is necessarily the case, independent of time and space. There is a perfect correlation between the event of heating and the event of boiling.
In order to resolve the inconsistency triad, Donaldson looks at token events such as Peter’s sudden desire to eat an ice-cream at a particular time and place. This event e has two properties: first, a mental property, being the onset of the intention to eat ice-cream. Second, a physical property, being the activation of a certain neural stage n in Peter’s brain. Event e causes event e*, a subsequent token event that is characterised by some further mental and physical properties involved in Peter’s actually purchasing an ice-cream. Importantly, the fact that event e is conceptualised as having two properties makes true both the causal and a reason explanation of event e*: on the physical level, neural stage n causes the body movements involved in the ice-cream purchase. The relationship between the cause and its effect is governed by some laws of nature. On the mental level, the desire to eat an ice-cream explains why Peter bought himself an ice-cream. It is the reason for the purchase transaction. Hence, there is one truthmaker for event*, namely event e, and two truths, i.e. the causal explanation and the reason explanation (Dyke 2009, chapter 6). The distinction between the two enables Davidson to resolve the inconsistency triad: The Principle of Causal Interaction is satisfied. Mental and physical properties are intertwined by association with one and the same event. The Principle of the Nomological Character of Causation can be upheld. Lawful causal connectivity is conceivable on the level of physical properties. The Principle of the Anomalism of the Mental is satisfied as well. Mental causation can be reasonably explained without reference to any correlation laws. Therefore, Davidson’s property dualism makes it possible to dissolve the appearance of a contradiction inherent in the inconsistent triad.
But how can the relationship between mental and physical properties be thought of? Ontologically speaking, Davidson is a monist. He rejects, for instance, Descartes’ dualism according to which there are two substances: mind and matter. For Davidson, physical matter is all there is. It is fundamental to reality. In Davidson’s monism any causally efficacious mental event has some physical description. In other words, mental properties have physical realisers. Without such physical realisers there would not be any mental properties. What happens on the physical level fixes the goings-on on the mental level. Even though he rejects substance dualism, Davidson clearly advocates a property dualism that privileges the physical over the mental. Philosophers would say the mental properties supervene on the physical. Since for causal explanations he puts the physical first, Davidson’s doctrine can be seen as a form of physicalism. This physicalism, however, must be a non-reductive one as he holds onto mental properties.
Importantly, all that Davidson commits himself to in the context of his non-reductive physicalism is token-identity, the identity of token mental states and token physical states. Given a specific event e, this particular mental state is that particular neural state n. What he denies is type-identity as this would require the existence of bridge laws that would make it possible to reduce mental state types to physical state-types. On Davidson’s account, one cannot translate mental descriptions into physical descriptions in a general and abstract fashion. One has to look at individual token events. The major advance of Davidson’s doctrine is that it enables him to uphold the Principle of the Anomalism of the Mental. The anomaly results from Davidson’s commitment to the idea that mental properties are not determined correlation laws that govern the world of causation, i.e. the physical world. Mental properties, on the other hand, are sufficient for reason explanations. (Dyke 2009, chapter 6). Someone who believes in Davidson’s ‘Anomalous Monism’, therefore, would find no contradiction in the inconsistent triad.
Reference
Davidson, David, Mental Events, 1970, in: David J. Chalmers (ed.), Philosophy of Mind – Classical and Contemporary readings, pp. 116-125, Oxford University Press, 2002
Dyke, Heather, From truth to reality: new essays in logic and metaphysics, New York, Routledge, 2009
Wetzel, Linda, “Types and Tokens”, The Stanford Encyclopedia of Philosophy (Spring 2014 Edition), Edward N. Zalta (ed.), URL = <https://plato.stanford.edu/archives/spr2014/entries/types-tokens/>, viewed on 31 May 2018
Thinking About Thinking 