Causal closure

Causal closure is a metaphysical theory about the nature of causation in the physical realm with significant ramifications in the study of metaphysics and the mind. In a strongly stated version, the causal closure principle (CCP) says that "Physical effects have only physical causes." - Agustin Vincente, p. 150

Those who accept the causal closure thesis tend to think that all entities that exist are physical entities (physicalists), but not necessarily. As Karl Popper says, "The physicalist principle of closedness of the physical ... is of decisive importance and I take it as the characteristic principle of physicalism or materialism."

Definition

Causal closure has stronger and weaker formulations.

The stronger formulations of causal closure assert that: "No physical event has a cause outside the physical domain." - Jaegwon Kim,. That is, the stronger formulations assert that for physical events, causes other than physical causes do not exist. (Physical events that are not causally determined may be said to have their objective chances of occurrence determined by physical causes.)

Weaker forms of the theory state that "Every physical event has a physical cause." - Barbara Montero, or "Every physical effect (that is, caused event) has physical sufficient causes" - Agustin Vincente. (According to Vincente, a number of caveats have to be observed, among which is the postulate that "physical entities" are entities postulated by a true theory of physics, a theory of which we are ignorant today. And that such a true theory "will not include mental (or in general, dubious) concepts".(Note 5, p. 168)) Or, that "if we trace the causal ancestry of a physical event we need never go outside the physical domain." - Jaegwon Kim, The weaker form of causal closure is synonymous with causal completeness, the notion that "Every physical effect that has a sufficient cause has a sufficient physical cause." That is, the weaker forms allow that in addition to physical causes, there may be other kinds of causes for physical events.

The notion of reductionism supplements causal closure with the claim that all events ultimately can be reduced to physical events. Under these circumstances, mental events are a subset of physical events and caused by them.

Importance

Causal closure is especially important when considering dualist theories of mind. If no physical event has a cause outside the physical realm, it would follow that non-physical mental events would be causally impotent in the physical world. However, as Kim has agreed, it seems intuitively problematic to strip mental events of their causal power. Only epiphenomenalists would agree that mental events do not have causal power, but epiphenomenalism is objectionable to many philosophers. One way of maintaining the causal power of mental events is to assert token identity non-reductive physicalism - that mental properties supervene on neurological properties. That is, that there can be no change in the mental without a corresponding change in the physical. Yet this implies that mental events can have two causes (physical and mental), a situation which apparently results in overdetermination (redundant causes), and denies strong causal closure. Kim argues that if the strong causal closure argument is correct, the only way to maintain mental causation is to assert type identity reductive physicalism - that mental properties are neurological properties.

Criticism

The validity of causal closure has long been debated. In modern times, it has been pointed out that science is based on removing the subject from investigations, and by seeking objectivity, creating a susceptibility to the subject-object problem. This outsider status for the observer, a third-person perspective, is said by some philosophers to have automatically severed science from the ability to examine subjective issues like consciousness and free will. A different attack upon causal closure discussed by Hodgson is to claim science itself does not support causal closure. Some philosophers have criticized the argument for causal closure by supporting teleology and mental-to-physical causation via a soul.

Ignoring Phenomena

There seem prima facie to be irreducible purpose-based (or teleological explanations) of some natural phenomena. For instance, the movement of a writer's fingers on the keyboard and a reader's eyes across the screen is irreducibly explained in reference to the goal of writing an intelligible sentence or of learning about the causal closure arguments, respectively. On the face of it, an exclusively non-teleological (descriptive) account of the neurological and biological features of hand movement and eye movement misses the point. To say, "I am moving my fingers because my brain signals are triggering muscle motion in my arms" is true, but does not exhaustively explain all the causes. Both are causes. In Aristotelian terms, a biological account explains the material cause, while the purpose-based account explains the final cause.

The causal closure thesis challenges this account. It attempts to reduce all teleological final (and formal) causes to efficient causes. Goetz and Taliaferro urge that this challenge is unjustified, partly because it would imply that the real cause of arguing for causal closure is neurobiological activity in the brain, not (as we know it is) the purpose-based attempt to understand the world and explain it to others.

Fallacious

One way of clarifying the causal closure argument is to add a premise specifying that there are no irreducible teleological causes. This, of course, is the attempted conclusion of the argument. Putting the conclusion as one of the premises of the argument is formally valid, but fallacious (begging the question). It is no more sound than the argument that, "I believe in the Bible because it is the written word of God through his prophets. Obviously, God would not lie to his prophets. After all, the Bible says so."

Trivial

Another way of clarifying the causal closure argument is to specify that: "Every physical effect [that has a physical cause] has a physical causes." But this is a tautology, and therefore true but trivial, like the statement "Every angel that has wings is an angel that has wings" or "Every white male who is bald is a bald white male."

See also

• Antireductionism
• Epiphenomenalism
• Physical determinism
• Reductionism
• Subject–object problem