Identity Theory and Mind-Brain Correlation

Most individuals in the philosophy of mind accept the Correlation Thesis, which serves as a foundational observation for discussing the relationship between the mental and the physical.
The thesis states that for every type of mental state a person experiences, there is a specific state of the brain (which may be unique to that individual's brain) that occurs at that exact time.
Formal Definition: A mental state occurs to an individual at a specific time if and only if a corresponding brain state occurs to that individual at that same time.
Implication: There cannot be even the most minute change in an individual's mental life without a corresponding change in their brain state.
Neutrality: The existence of a correlation does not automatically favor physicalism over dualism.
- Substance Dualists can agree to the correlation if they interpret the necessity as nomological necessity (contingent laws of nature) rather than logical necessity (an identity or necessary connection).
- Under this view, mental states and brain states simply fit together with a lawful regularity.

In nature, correlations between two variables ( $X$ and $Y$ ) typically require an explanation. The lecture provides four primary ways variables can be correlated:
Causality: One variable causes the other.
- Example: The correlation between drinking alcohol and drunkenness exists because drinking causes the state of being drunk.
Common Cause: A third, external factor causes both variables to fluctuate together.
- Example: The correlation between ice cream sales and violent crime rates. This is not because ice cream causes crime (or criminals celebrate with ice cream at Dairy Queen), but because summer heat increases both the desire for ice cream and human irritability/aggression (particularly noted in environments like Phoenix, Arizona).
Identity: The variables are correlated because they are actually the same thing described by different names.
- Example: Sicknesses and illnesses are perfectly correlated because they are identical events.
Two Aspects of the Same Event: The correlation exists because two terms describe the same event from different perspectives.
- Example: The correlation between killings and "dyings." Whether an event is caused by a virus, old age, or another person, every killing corresponds to a dying. They are not two separate events in the world but two ways to describe one event based on perspective.

The Brute Fact Option: It is possible that a correlation has no explanation and is simply a coincidence or an unexplainable reality.
- Example: The statistical correlation between U.S. margarine purchases and the divorce rate in Maine. There is likely no causal or essential connection; it is just a "crazy correlation."
Emergentism: Jaeghwon Kim and David Chalmers often describe emergentism as a view where the mind-brain correlation is a "brute" or "unexplainable" fact.
Speaker's Critique of the "Brute" Label: The speaker suggests that emergentists do not necessarily believe the correlation is unexplainable. Rather, they believe that one specific type of explanation—physicalism (the claim that mental and physical things share the same essential nature)—is unavailable.
An alternative explanation for emergentists is that the physical is responsible for the mental; the mental emerges from the physical. This is viewed as a useful, non-ad-hoc explanation applicable in domains outside the mental-physical relationship.

The Identity Theory posits that the simplest explanation for the mind-brain correlation is that the mind and the brain are identical.
Core Claim: Mental states are brain processes. Every type of mental state is a type of brain process, and every token (individual instance) mental state is a token brain process.
J.J.C. Smart: A prominent advocate of identity theory who utilized an Occam's Razor (parsimony) argument.
Nomological Danglers: Smart argued against any theory that maintains "nomological danglers." These are laws of nature that link high-level phenomena (like the mental) to low-level phenomena (the physical) without the high-level phenomena being reducible to the lower level.
- In science, we do not find independent laws of chemistry that are disconnected from physics; chemistry is explained in terms of fundamental physics.
- Biological laws (such as those regarding reproduction) are explained through chemistry and physics.
- Smart concludes that brute laws linking the mental to the physical would be unique "danglers" that violate the principle of simplicity.

Jaeghwon Kim provides an argument for the Identity Theory based on the Principle of Causal Closure of the Physical Domain.
The Principle: If any physical event ( $P$ ) is caused, then it has a sufficient physical cause ( $C_p$ ).
Kim's Argument Structure:
1. Mental events cause physical effects (e.g., a belief and desire to lecture causes the physical production of sound waves).
2. Every physical event that has a cause has a sufficient physical cause (Causal Closure).
3. Therefore, mental events must be physical events.

The speaker argues that Kim's argument is invalid depending on how one defines a "sufficient physical cause." There are three possible interpretations:

Logical Entailment: $X$ is a sufficient condition of $Y$ if $X$ necessitates $Y$ by logic or laws of nature.
- Critique: Entailment relations are not the same as causal relations. The fact that $A$ entails $B$ does not mean $A$ causes $B$ or that $B$ has no other cause.
Sufficiency (Intuitive Sense): Nothing more than $X$ is needed for $Y$ to occur.
- Critique: This allows for Overdetermination.
- The Firing Squad Example: If two soldiers shoot simultaneously (one to the head, one to the heart), both shots are individually sufficient to cause death. In this case, there are two sufficient causes.
- Thus, there could be a sufficient physical cause and a sufficient mental cause for the same action without the two being identical.
Exclusive Cause: $X$ is sufficient for $Y$ meaning $X$ is the only cause of $Y$.
- Critique: This would make Kim's argument valid, but the principle of causal closure becomes implausible.
- To find a single, exclusive cause for an event (like a lecture), one would have to include the entire state of the universe (gravity, electromagnetism, the existence of the speaker's parents, the fact that an asteroid has not hit the speaker).
- If the principle is defined this way, it essentially just restates physicalism (every physical event is caused only by a prior physical state of the universe), making the argument circular and unproductive.

While Kim's argument is influential, the speaker finds it less persuasive than the simplicity-based arguments.
The course will next examine Machine Functionalism as an alternative functionalist approach to physicalism.