Anomalous Monism

Anomalous monism, developed by Donald Davidson, combines three claims: mental events causally interact with physical events; events related as cause and effect fall under strict laws; and there are no strict psychophysical laws connecting mental and physical types. Davidson concludes that each causally interacting mental event is identical with some physical event, although mental kinds do not reduce to physical kinds.

The view is monist about events and anomalous about mental description. It avoids interaction between separate substances and preserves the autonomy of reasons explanation. Its central objection is that event identity may leave mental properties causally irrelevant: the event enters a strict law only under a physical description, so in what sense does it cause action because of what the subject believed?

The three principles

Davidson begins with principles that appear jointly inconsistent:

1. Causal interaction: at least some mental events cause physical events and vice versa.
2. Nomological character of causality: causally related events instantiate a strict law under some description.
3. Anomalism of the mental: there are no strict deterministic laws connecting mental types with physical types.

If a mental event $m$ causes physical event $p$, principle 2 says they instantiate a law. Principle 3 says the law cannot be psychophysical under their mental descriptions. Therefore $m$ must have a physical description under which it enters a physical law. The mental event is a physical event:

$$m=p_m,$$

without the mental predicate being identical with a physical predicate.

This is token identity without type identity.

Events under descriptions

One event can be described as "the pressing of the switch," "the movement of a finger," and "a neural-muscular process." Causation relates events, not descriptions. Laws, however, relate events as described under predicates suitable for generalisation.

A person's deciding to leave may be identical with a neural event. It causes bodily motion as one event, even though only its physical description belongs to a strict law. This blocks event-level exclusion: there are not two causes.

The distinction also preserves reasons explanation. Calling the event a decision places it in a rational pattern of beliefs, desires, and actions even if no law pairs all decisions of that content with one neural type.

Why the mental is anomalous

Davidson does not mean mental events are random or inexplicable. Anomalous means not captured by strict, exceptionless laws of the kind sought in fundamental physics.

Mental attribution is governed by constitutive principles of rationality. To interpret a person as believing and desiring, one must locate their attitudes in a largely coherent pattern responsive to evidence and action. Attribution is holistic: the content of one belief depends on many others and on the interpreter's assumptions about the subject's reasons.

Physical predicates are not constitutively governed by rationality in this way. There is no finite bridge law connecting each holistic mental type with a physical type. Psychological generalisations can be useful and exception-tolerant without becoming strict laws.

Supervenience

Davidson also holds that mental properties supervene on physical properties: no two events can be alike in all physical respects while differing mentally. This secures dependence without reduction.

Supervenience alone does not explain why the mental pattern follows from the physical, as The Mind-Body Problem emphasises. In anomalous monism, token identity and interpretive principles do additional work. Still, the relation between physical constitution and rational interpretation remains less explicit than in functional realisation theories.

Reasons as causes

Davidson argues that a primary reason - roughly, a pro-attitude toward actions of a kind plus a belief that this action is of that kind - rationalises an action by causing it. If someone turns on the light because they want illumination and believe flipping the switch will provide it, the reason both makes the action intelligible and belongs to its causal history.

This rejects non-causal accounts on which reasons merely justify or render action intelligible. Causal connection distinguishes acting for a reason from merely having a reason that happens to fit the action.

Davidson also denied that reason explanations require strict laws. Singular causal relations can hold even when the explanatory vocabulary is not nomological. This is essential to anomalous monism.

The qua problem

Suppose an event is both a belief and a neural firing pattern. It causes movement under a physical law. Did it cause the movement qua belief, in virtue of its mental properties, or only qua physical?

Critics argue anomalous monism guarantees only that mental events are causes, not that mental properties are causally relevant. If content could vary while the causally efficacious physical properties stayed fixed, the explanation citing content would not track the cause.

Davidsonian replies resist "causing under a description." Events cause regardless of which true description an explanation uses. Mental descriptions can identify the cause that answers a contrastive question, even though physical descriptions connect it to a strict law.

The reply is strongest if causal relevance belongs primarily to events. Property-based theories demand more: a reason should explain the effect because of its content. That demand motivates interventionist and proportionality accounts.

Strict laws and contemporary science

The premise that causation requires strict laws is contested. Special sciences use ceteris paribus generalisations, mechanisms, probabilistic models, and interventions. If causes need not instantiate exceptionless laws, the route from mental causation to token physical identity loses force.

Conversely, fundamental physical laws may not determine unique outcomes. Davidson's argument can be reformulated using physically complete probabilistic laws, but its original nomological framework is not mandatory for causal realism.

Anomalous monism remains influential less as a deduction than as a model of levels: one event can sustain physical causal explanation and rational interpretation without a type-by-type reduction.

Holism and interpretation

The anomalism thesis protects the normative character of thought. Beliefs are not identified independently and then connected by laws; they are attributed within a network constrained by coherence, truth, and rational action.

This can seem overly idealising. Humans reason badly, compartmentalise, and hold contradictory beliefs. Davidson needs only enough rationality to make interpretation possible, not perfect rationality. The threshold and its implications for animals or artificial systems remain contested.

The view also risks making content depend on an interpreter. Davidson treats interpretive indeterminacy as compatible with objective patterns, but theorists seeking determinate internal representations may find the account too external and holistic.

Assessment

Anomalous monism's durable insight is that causal monism need not entail explanatory monism. Its unresolved question is whether true and useful mental descriptions are enough for mental causation, or whether content must be independently shown to make a difference.

Selected references

• Davidson, Donald. "Actions, Reasons, and Causes" (1963).
• Davidson, Donald. "Mental Events" (1970).
• Davidson, Donald. Essays on Actions and Events (1980).
• Kim, Jaegwon. "Can Supervenience and 'Non-Strict Laws' Save Anomalous Monism?" (1993).