“Anomalous Monism” is a philosophical thesis thesis about the mind-body relationship. It was first proposed by Donald Davidson in his 1970 paper Mental events. The theory is twofold and states that mental events are identical with physical events (this is physicalism, a form of materialism) and that the mental is anomalous, i.e. under their mental descriptions these mental events are not regulated by strict physical laws. Hence, Davidson proposes an identity theory of mind without the reductive bridge laws associated with the type-identity theory. Since the publication of his paper, Davidson has refined his thesis and both critics and supporters of anomalous monism have come up with their own characterizations of the thesis, many of which appear to differ from Davidson’s.

Considering views about the relation between the mental and the physical as distinguished first by whether or not mental entities are identical with physical entities, and second by whether or not there are strict psychophysical laws, we arrive at a fourfold classification: (1) nomological monism, which says there are strict correlating laws, and that the correlated entities are identical (which is often called materialism); (2) nomological dualism (interactionism, parallelism, epiphenomenalism ); (3) anomalous dualism, which holds there are no laws correlating the mental and the physical, and the substances are discrete (Descarte’s dualism); and (4) anomalous monism, which allows only one class of entities, but denies the possibility of definitional and nomological reduction. Davidson’s claim was that anomalous monism is the answer to the mind-body problem.

Since every mental event is some physical event or other, the idea is that someone’s thinking at a certain time, for example, that snow is white, is a certain pattern of neural firing in their brain at that time, an event which can be characterized as both a thinking that snow is white (a type of mental event) and a pattern of neural firing (a type of physical event). There is just one event that can be characterized both in mental terms and in physical terms. If mental events are physical events, they can at least in principle be explained and predicted, like all physical events, on the basis of laws of physical science. However, according to anomalous monism, events cannot be so explained or predicted as described in mental terms (such as “thinking”, “desiring” etc), but only as described in physical terms: this is the distinctive feature of the thesis as a brand of physical monism.

Davidson makes what even his opponents have called an “ingenuous” argument for his version of non-reductive physicalism. The argument relies on the following three intuitively compelling principles:

  1. The principle of causal interaction: there exist both mental-to-physical as well as physical-to-mental causal interactions.
  2. The principle of the nomological character of causality: all events are causally related through strict laws.
  3. The principle of the anomalism of the mental: there are no psycho-physical laws which relate the mental and the physical as just that, mental and physical.