Physical Monism and Related Theories

Physical Monism

• Physical Monism is related to:
  • Weak materialism.
  • Identity theory.
  • The idea that mental events are causes.
  • Dualistic Interactionism.
  • Epiphenomenalism.

The Identity Thesis (IT) and the Correlation Thesis (CT)

• The Identity Thesis (IT) is defined as mental events being numerically identical to brain events. For example, Susan's thinking about cats is numerically identical to a brain event x happening in Susan's brain.
• The Correlation Thesis (CT) is defined as for a human mental event M, there is some corresponding brain event happening in a human brain.
• Logical Relation:
  • Understanding the logical connection between IT and CT.
  • Considering who can accept CT and who accepts IT.

Correlation, Causation, and Identity: The Flicking Lights Example

• The experience of lights going on and off is correlated with someone flicking the light switch.
• Flicking the light switch is considered the cause of the experience of the lights going on and off.
• Experiencing the lights going on and off is correlated with others having the same experience, but one person's experience is not the cause of another person's experience.

How Mental and Brain Events Correlate

• The correlation could be that of identity, where mental event M (e.g., thinking about unicorns) is numerically identical to a brain event if the identity thesis is correct.
• The correlation between the mental and physical can be as effect to cause, where mental event M is an effect of brain event B and M and B are not numerically identical. It can also be cause to effect, where mental event M1 is the cause of brain event B1, and M1 and B1 are not numerically identical, if epiphenomenalism is correct.
• The correlation can be as two different contributing causes of the same effect; for example, a person's thinking about the nature of triangles (a mental event) has brain events as a cause, such as an image of a triangle, but this is not a sufficient cause. Thinking about the nature of triangles involves more than the brain, potentially involving the immaterial mind or soul as a cause (since the nature of triangles can’t be sensed or imagined).

A Flawed Argument for the Identity Thesis

• Premise 1: If some part of the brain is active whenever one engages in mental activity (e.g., thinking, feeling, choosing), i.e., there is a correlation between mental activity and brain activity, then mental activity is identical to brain activity.
• Premise 2: Some part of the brain is active whenever one engages in mental activity, i.e., there is a correlation between mental activity and brain activity.
• Conclusion: Therefore, mental activity is identical to brain activity [from (1) and (2)].

The Last Man Standing Argument for Physical Monism (PM)

• Premise 1: DI (Dualistic Interactionism) or E (Epiphenomenalism) or PM (Physical Monism) [assumption].
• Premise 2: Mental events can directly cause physical events, and physical events can directly cause mental events. Beliefs, desires, and volitions are genuine causes of physical events in the external world (the interaction intuition).
• Premise 3: The Causal Interaction Problem poses a problem for DI [assumption].
• Conclusion 1: Therefore, not DI [from (3) and (4)].
• Premise 4: E is incompatible with (2).
• Conclusion 2: Therefore, not (E) [from (2), (3), and (6)].
• Premise 5: PM is consistent with (2), and the Causal Interaction Problem is not a problem for PM.
• Conclusion 3: Therefore, PM [from (1), (4), (6), and (7)].

Revisiting the Causal Interaction Problem against DI

• Premise 1: If DI, then a non-physical substance causally interacts with a physical substance (or non-physical events cause physical events and vice versa).
• Premise 2: Therefore, if DI is plausible, then we have to be able to explain how a non-physical substance (event) could causally interact with a physical substance (event) [from (1)].
• Premise 3: But we can’t offer such an explanation [assumption].
• Conclusion: Therefore, DI is not plausible [from (2) and (3), Modus Tollens (MT)].

A Defeater for the Causal Interaction Problem

• Premise 1: If we should reject DI because we don’t understand how a non-physical thing can causally interact with a physical thing, then, to be consistent, we should reject any position that posits a causal relation between an x and a y where we don’t understand how x causally interacts with y.
• Premise 2: We don’t understand how physical things causally interact with other physical things [assumption].
• Conclusion: Therefore, if we should reject DI because we don’t understand how a non-physical thing can causally interact with a physical thing, then we should reject other positions, since they posit a causal relation between physical things, where we don’t understand how physical things cause effects in other physical things [from (1) and (2)].

Three Potential Problems for Physical Monism

• The problem for the identity thesis.
• The problem of personal identity over time.
• The problem of freewill for physical monism.

Potential Problem #1 for PM: The Falsity of the Identity Thesis Argument

• Premise 1: If physical monism is true, then the identity thesis is true [assumption].
• Premise 2: If the identity thesis is true, then human mental events are numerically identical to brain events [assumption].
• Premise 3: Human, mental events are not numerically identical to physical events.
• Conclusion 1: Therefore, the identity thesis is false [from (2) and (3), MT].
• Conclusion 2: Therefore, physical monism is false [from (1) and (4), MT].

An Argument for Mental Event/Brain Event Dualism: The Mental and Brain Events Have Different Properties Argument

• Mental event/brain event dualism is defined as it not being the case that mental events are numerically identical to brain events and mental events are real.
• Brain events are, in principle, observable by the ordinary senses, at least via a brain scanning device.
• Mental events themselves (e.g., the experience of seeing a red ball, the experience of imagining a red ball, the act of thinking that 2+2=4) are, in principle, not observable by the ordinary senses, but rather by introspection.
• Brain events have the essential property of being observable, whereas mental events do not [from (2) and (3)].
• Premise: If x and y have different essential properties, then x and y are not numerically identical [assumption].
• Conclusion 1: Therefore, it is not the case that mental events are numerically identical to brain events [from (4) and (5)].
• Premise: Mental events are real [assumption].
• Conclusion 2: Therefore, mental event/brain event dualism is true [from (1), (6), and (7)].

Against Physical Monism from the Reality of Personal Identity Over Time

• Premise 1: A compound physical object is numerically identical to an aggregate of physical simples [atomistic or reductionist assumption made by materialists such as Physical Monists].
• Premise 2: If an aggregate A and an aggregate A1 have numerically different parts, then A and A1 are not numerically identical aggregates [assumption].
• Premise 3: Therefore, if a compound physical object x and a compound physical object y are composed of numerically different parts, then x and y are not numerically identical physical objects [from (1) and (2)].
• Premise 4: Human organisms constantly undergo changes with respect to their parts and total replacement of their parts approximately every seven years [assumption].
• Premise 5: Therefore, if human persons are identical to human organisms, then no human person lasts long enough to be held morally accountable for their actions or accomplish projects or maintain friendships and marriages, etc.
• Premise 6: But human persons sometimes do last long enough to be held morally accountable for their actions or accomplish projects or maintain friendships and marriages, etc. [assumption].
• Conclusion 1: Therefore, it is not the case that human persons are identical to human organisms [from (5) and (6), MT].
• Premise 7: If Physical Monism is true, then human persons are identical to human organisms [self-evident].
• Conclusion 2: Therefore, Physical Monism is false [from (7) and (8), MT].

Potential Problem #3 for PM: The Argument from Personal Agency and Libertarian Freewill

• Premise 1: If (a) physical monism is true, then (b) human mental acts (e.g., acts of belief, desire, and freewill) are numerically identical to micro-physical actions, i.e., certain chemical reactions in the brain [self-evident].
• Premise 2: Chemical reactions are sub-personal, i.e., they do not have persons as their causes, but other chemical reactions; any so-called personal act is just another chemical reaction in the brain [assumption made by PM].
• Premise 3: Human acts of belief, desire, and libertarian freewill are acts of persons and not sub-personal [assumption].
• Premise 4: Therefore, if (b) human mental acts (e.g., acts of belief, desire, and freewill) are numerically identical to micro-physical actions, i.e., certain chemical reactions in the brain, then (c) human persons (e.g., you and I) never engage in acts of belief, desire, or libertarian free will [from (2) and (3)].
• Premise 5: Therefore, if (a) physical monism, then (c) human persons (e.g., you and I) never engage in acts of belief, desire, or libertarian free will [from (1) and (4)].
• Premise 6: Human persons (e.g., you and I) do sometimes engage in acts of belief, desire, and libertarian free will [assumption].
• Conclusion: Therefore, physical monism is false [from (5) and (6), MT].