Jaquan Kim’s Arguments on Mental Causation

Introduction to Jaquan Kim’s Arguments on Mental Causation

• The lecture focuses on the second half of Chapter 7 of Jaquan Kim’s textbook, titled "Mental Causation."

• The discussion centers on a pair of arguments famously associated with Kim: the exclusion argument and the supervenience argument.

• These arguments date back to the 1980s and have generated a vast literature that continues to be debated today.

• The primary source material for these arguments in the paperback edition of Kim's textbook is found on pages 214 through 220.

The Supervenience Argument

• The supervenience argument is presented as the simpler of the two arguments. Its goal is to demonstrate that if one accepts mental-to-mental causation and the principle of supervenience, one must also accept mental-to-physical causation.

• This argument targets the nonreductive physicalist who accepts supervenience but wants to deny radical epiphenomenalism.

• Radical Epiphenomenalism: The claim that there is no mental-to-mental causation; the mental is essentially "on for the ride" and possesses no causal power.

Illustrative Examples of Causal Chains

1. Physical-to-Mental: A mosquito bites you (physical event), causing an itch (mental event).

2. Mental-to-Mental: The sensation of an itch ($m_1$) causes the formation of a desire to scratch ($m_2$). These are distinct states: an itch is a sensation, while a desire is a cognitive state.

3. Mental-to-Physical: The desire to scratch ($m_2$) causes the physical action of scratching ($p_2$).

The Logic of the Supervenience Argument

• Suppose we have two mental states, an itch ($m_1$) and a desire to scratch ($m_2$). We assume $m_1$ causes $m_2$.

• According to supervenience, every mental state has an underlying physical state that realizes it. Let $m_1$ supervene on brain state $p_1$, and $m_2$ supervene on brain state $p_2$.

• Nonreductive physicalists maintain that these states are distinct ($m_1 \neq p_1$ and $m_2 \neq p_2$).

• Counterfactual Dependency: A general truth about causation states that if a cause causes an effect, then were it not for the cause, the effect would not have occurred. Thus, if $m_1$ causes $m_2$, then had $m_1$ not occurred, $m_2$ would not have occurred.

• If $m_2$ supervenes on $p_2$, then $p_2$ necessitates $m_2$. There is no possible world where $p_2$ occurs but $m_2$ does not.

• For the counterfactual "If $m_1$ had not occurred, $m_2$ would not have occurred" to remain true, it must be that $m_1$ causes $p_2$. If $m_1$ did not occur but $p_2$ still occurred, then $m_2$ would still occur (because $p_2$ guarantees it), making the initial causal claim false.

• Therefore, to maintain mental-to-mental causation ($m_1 \rightarrow m_2$), one must accept that the mental state counterfactually causes the underlying physical state of the effect ($m_1 \rightarrow p_2$).

Definitions of Causality: Counterfactual and Sufficient Causes

• Counterfactual Cause: A cause where the effect depends on the cause; if the cause is removed, the effect does not happen.

• Sufficient Cause: A cause that not only contributes to the effect but guarantees the outcome.

• Example of a Non-Sufficient Cause: Watering plants is a cause of their growth, but it is not sufficient. Growth also requires sunlight and the absence of disease or frost. Watering does not guarantee the outcome.

• Example of a Sufficient Cause: Laws of physics, such as gravity. If objects of mass $m_1$ and $m_2$ are present, the law of gravity guarantees a specific gravitational pull between them.

The Principle of Causal Closure

• The Exclusion Argument relies on the Principle of Causal Closure (PCC).

• Definition: Every physical event which has a cause at time $t$ has a sufficient physical cause at time $t$.

Kim’s Clarifications on Causal Closure

1. It does not strictly mandate physicalism. It is compatible with Cartesian dualism (immaterial minds) as long as those minds are not required for physical events to occur; any physical effect caused by a mind must also have a sufficient physical cause at that same time.

2. It does not require Determinism (the thesis that every physical event has a sufficient physical cause). For example:

   • If the Big Bang was the first event and had no cause, PCC is not violated because PCC only applies to events that have a cause.

   • If quantum events are indeterminate and have no cause at all, PCC is not violated.

Motivations for Accepting Causal Closure

• If closure fails, theoretical physics would be in principle incomplete, a prospect most physicists reject.

• Research programs in the physical sciences presuppose a principle similar to closure.

• It gives meaning to the view that the physical domain is all-encompassing and that physics is the basic science.

The Exclusion Argument

• The argument builds on the conclusion of the supervenience argument ($m_1$ causes $p_2$) and the Principle of Causal Closure (PCC).

• If the physical event $p_2$ has a cause ($m_1$), then by PCC, it must also have a sufficient physical cause at that same time (call it $p_1$ or some other physical state).

• This leads to three possibilities regarding the cause of $p_2$:

  1. Reductive Physicalism (Identity Theory): The mental cause $m_1$ is identical to the physical cause $p_1$. There is only one cause.

  2. Overdetermination Case A: The subvening base $p_1$ is the sufficient physical cause, meaning $p_2$ has two distinct causes: $m_1$ and $p_1$.

  3. Overdetermination Case B: Some other distinct physical event at time $t$ is the sufficient cause of $p_2$, again resulting in two causes ($m_1$ and the other event).

The Exclusion Principle and Overdetermination

• The Exclusion Principle: No event has two or more distinct sufficient causes occurring at the same time unless it is a genuine case of overdetermination.

• Genuine Overdetermination: Rare instances that are either intentionally planned (e.g., a firing squad where multiple bullets are sufficient to cause death) or coincidental (e.g., a person being struck by lightning while simultaneously drowning).

• Kim argues that it is implausible to suggest that mental-physical causation is a case of constant, widespread overdetermination in billions of people. This would require a "pre-established harmony" similar to that proposed by Leibniz.

• Conclusion: If we reject widespread overdetermination and radical epiphenomenalism, and accept causal closure, we must conclude that every mental event is identical to a physical event ($m_1 = p_1$). This leads to Reductive Physicalism.

Critical Responses and Objections

Counterfactual vs. Sufficient Causation

• One could argue that the supervenience argument only proves $m_1$ is a counterfactual cause of $p_2$, not a sufficient one. If $p_2$ has one sufficient physical cause and one mental counterfactual cause, this may not violate the Exclusion Principle, as it is not a case of two "sufficient" causes.

• Kim might ask what "work" the mental state is doing if the physical state already guarantees the outcome. This assumes a metaphorical view of causation as "work."

The Dependence of Causes

• A nonreductive physicalist could argue that $m_1$ and $p_1$ are not independent. If $m_1$ supervenes on $p_1$, you cannot have $p_1$ without $m_1$. Thus, if $m_1$ didn't occur, $p_1$ wouldn't have occurred, and $p_2$ wouldn't have occurred. There is no contradiction or problematic overdetermination if the causes are necessitated by one another.

The Levels of Reality / Baseball Example

• Some argue that overdetermination is common and non-problematic when involving different levels of description.

• Example: If a baseball is thrown through a window, one could say the baseball caused the window to break, the rubber in the ball caused it, and the particles in the ball caused it.

• These are not identical (a table is not strictly identical to its particles if the particles can change but the table remains), yet we don't view this as a "coincidence" or "massive planning" by an evil genius. Similarly, the itch and the brain state are dependent, not independent, making overdetermination less problematic.

Challenges to Causal Closure

• Kim’s defense of PCC is seen by some as moving from methodology (how we do science) to metaphysics (how the world is).

• A scientist might methodologically assume a physical cause exists to stay motivated in research, but they may not be committed to the metaphysical dogma that a sufficient physical cause must exist for every event.

• Kim’s claim that physics is the "basic science" (e.g., explaining biology through chemistry and radiation) does not necessarily require that every event has a sufficient physical cause at the time it occurs.

The Conflict with Quantum Indeterminacy

• Kim claims PCC is compatible with indeterminism, but the lecture argues this is doubtful.

• The Radioactive Sand Experiment:

  • Suppose you move a shovel of radioactive sand from the back porch to the front porch (physical cause at time $t_1$).

  • The sand continues to undergo indeterministic radioactive decay at the quantum level.

  • The decay has a physical cause (being moved to the porch), but it does not have a sufficient physical cause because the process is truly indeterministic (no prior state guarantees the outcome).

  • If an event has a cause but no sufficient physical cause, Kim's PCC is false.

• Modifying the PCC: One could redefine "sufficient physical cause" to mean "all that is needed" rather than "that which guarantees." Under this definition, the physical story is the whole story, even if it doesn't guarantee the outcome. However, if this definition is used, the problem of overdetermination disappears because having "all that is needed" plus "another cause" is not philosophically problematic.