Libertarianism is one of the main philosophical positions related to the problems of free will and determinism, which are part of the larger domain of metaphysics.[1] In particular, libertarianism, which is an incompatibilist position,[2][3] argues that free will is logically incompatible with a deterministic universe and that agents have free will, and that, therefore, determinism is false.[4] Although compatibilism, the view that determinism and free will are not logically incompatible, is the most popular position on free will amongst professional philosophers,[5] metaphysical libertarianism is discussed, though not necessarily endorsed, by several philosophers, such as Peter van Inwagen, Robert Kane, Robert Nozick,[6]Carl Ginet, Hugh McCann, Harry Frankfurt, E.J. Lowe, Alfred Mele, Roderick Chisholm, Daniel Dennett,[7] Timothy O'Connor, Derk Pereboom, and Galen Strawson.[8]

The term "libertarianism" in a metaphysical or philosophical sense was first used by late Enlightenment free-thinkers to refer to those who believed in free will, as opposed to determinism.[9] The first recorded use was in 1789 by William Belsham in a discussion of free will and in opposition to "necessitarian" (or determinist) views.[10][11] Metaphysical and philosophical contrasts between philosophies of necessity and libertarianism continued in the early 19th century.[12]

Metaphysical libertarianism is one philosophical view point under that of incompatibilism. Libertarianism holds onto a concept of free will that requires the agent to be able to take more than one possible course of action under a given set of circumstances.

Accounts of libertarianism subdivide into non-physical theories and physical or naturalistic theories. Non-physical theories hold that the events in the brain that lead to the performance of actions do not have an entirely physical explanation, and consequently the world is not closed under physics. Such interactionist dualists believe that some non-physical mind, will, or soul overrides physical causality.

Explanations of libertarianism that do not involve dispensing with physicalism require physical indeterminism, such as probabilistic subatomic particle behavior theory unknown to many of the early writers on free will. Physical determinism, under the assumption of physicalism, implies there is only one possible future and is therefore not compatible with libertarian free will. Some libertarian explanations involve invoking panpsychism, the theory that a quality of mind is associated with all particles, and pervades the entire universe, in both animate and inanimate entities. Other approaches do not require free will to be a fundamental constituent of the universe; ordinary randomness is appealed to as supplying the "elbow room" believed to be necessary by libertarians.

Free volition is regarded as a particular kind of complex, high-level process with an element of indeterminism. An example of this kind of approach has been developed by Robert Kane,[13] where he hypothesises that,

In each case, the indeterminism is functioning as a hindrance or obstacle to her realizing one of her purposesa hindrance or obstacle in the form of resistance within her will which has to be overcome by effort.

Although at the time C. S. Lewis wrote Miracles,[14]Quantum Mechanics (and physical indeterminism) was only in the initial stages of acceptance, he stated the logical possibility that if the physical world was proved to be indeterministic this would provide an entry (interaction) point into the traditionally viewed closed system, where a scientifically described physically probable/improbable event could be philosophically described as an action of a non-physical entity on physical reality.

Nozick puts forward an indeterministic theory of free will in Philosophical Explanations.[6]

When human beings become agents through reflexive self-awareness, they express their agency by having reasons for acting, to which they assign weights. Choosing the dimensions of one's identity is a special case, in which the assigning of weight to a dimension is partly self-constitutive. But all acting for reasons is constitutive of the self in a broader sense, namely, by its shaping one's character and personality in a manner analogous to the shaping that law undergoes through the precedent set by earlier court decisions. Just as a judge does not merely apply the law but to some degree makes it through judicial discretion, so too a person does not merely discover weights but assigns them; one not only weighs reasons but also weights them. Set in train is a process of building a framework for future decisions that we are tentatively committed to.

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Libertarianism: Definition from Answers.com