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Classical incompatibilists hold that determinism leaves no room for free will.

Incompatibilism is the view that the thesis of determinism is logically incompatible with the classical thesis of free will. The term was coined in the 1960s, most likely by philosopher Keith Lehrer.[1][2] The term compatibilism was coined (also by Lehrer) to name the view that the classical free will thesis is logically compatible with determinism, i.e. it is possible for an ordinary human to exercise free will (the freedom-relevant ability to do otherwise), even in a universe where determinism is true. These terms were originally coined for use within a research paradigm that was dominant among academics during the so-called "classical period" from the 1960s to 1980s,[1] or what has been called the "classical analytic paradigm".[3] Within the classical analytic paradigm, the problem of free will and determinism was understood as a compatibility question: "Is it possible for an ordinary human to exercise free will (classically defined as an ability to do otherwise) when determinism is true?"[4] Those working in the classical analytic paradigm who answered "no" were incompatibilists in the original, classical-analytic sense of the term, now commonly called classical incompatibilists; they proposed that determinism precludes free will because it precludes the ability to do otherwise. Those who answered "yes" were compatibilists in the original sense of the term, now commonly called classical compatibilists.[5] Given that classical free will theorists (i.e. those working in the classical analytic paradigm) agreed that it is at least metaphysically possible for an ordinary human to exercise free will,[6][7] all classical compatibilists accepted a compossibilist account of free will (i.e. a compossibilist interpretation of the ability to do otherwise) and all classical incompatibilists accepted a libertarian (a.k.a. libertarianist) account of free will (i.e. a libertarian/libertarianist interpretation of the ability to do otherwise).

The classical analytic paradigm has fallen out of favor over the last few decades, largely because philosophers no longer agree that free will is equivalent to some kind of ability to do otherwise;[8] many hold that it is, instead, a type of sourcehood that does not require an ability to do otherwise.[9] The number of philosophers who reject the classical assumption of anthropocentric possibilism, i.e. the view that it is at least metaphysically possible for a human to exercise free will, has also risen in recent years.[10][11] As philosophers adjusted Lehrer's original (classical) definitions of the terms incompatibilism and compatibilism to reflect their own perspectives on the location of the purported "fundamental divide" among free will theorists, the terms incompatibilism and compatibilism have been given a variety of new meanings. At present, then, there is no standard meaning of the term incompatibilism (or its complement compatibilism).

Definition

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On one recent taxonomy, there are now at least three substantively different, non-classical uses of the term incompatibilism, namely: neo-classical incompatibilism, post-classical incompatibilism (a.k.a. incompossibilism), and anti-classical incompatibilism. Correspondingly, there are neo-classical, post-classical (compossibilist), and anti-classical versions of compatibilism as well.[12] Neo-classical incompatibilism is a two-tenet view: incompossibilism is true (i.e. it is metaphysically impossible for an ordinary human to act freely when determinism is true), and determinism-related causal/nomological factors preclude free will (which explains why incompossibilism is true).[13][14] Correspondingly, neo-classical compatibilism is the two-tenet view that: the negative, non-explanatory tenet of neo-classical incompatibilism is false (i.e. compossibilism is true), and that the positive, explanatory tenet of neo-classical incompatibilism is false. Anti-classical incompatibilism is the explanatory thesis of neo-classical incompatibilism; anti-classical incompatibilism is neutral on the truth-value of incompossibilism.[15] Correspondingly, anti-classical compatibilism is the negation of neo-classical incompatibilism's positive tenet, i.e. anti-classical compatibilism is the contradictory of anti-classical incompatibilism. Post-classical incompatibilism is just the negative, non-explanatory thesis of neo-classical incompatibilism; this view is neutral on whether the positive, explanatory thesis of neo-classical incompatibilism is true. (Put another way, on the post-classical redefinition of incompatibilism, it is just an alternative name for incompossibilism, a view which is completely silent on whether determinism-related causal factors are relevant to free will or are a total "red herring" in discussions of free will.) Correspondingly, post-classical compatibilism is identical to compossibilism (i.e. on the post-classical redefinition of compatibilism, it denotes mere compossibilism).[16][17][18]

The ambiguity of incompatibilism can be a source of confusion because arguments with very different (even inconsistent) conclusions are currently lumped together under the umbrella phrase "arguments for incompatibilism". For example, it is easy for the casual reader to overlook that some arguments for post-classical incompatibilism (a.k.a. incompossibilism) are not arguments for neo-classical incompatibilism on the grounds that the argument does not aim to support the latter's explanatory tenet (a.k.a. anti-classical incompatibilism).[19][20][21][22] Other arguments support post-classical incompatibilism (a.k.a. incompossibilism) but conclude that neo-classical incompatibilism is false on the grounds that its explanatory tenet (a.k.a. anti-classical incompatibilism) is false.[23][15][24] Arguments in the last category conclude that people lack free will when determinism is true but not at all because determinism is true (i.e. not at all because certain causal/nomological factors obtain); most propose that the real threat to free will is that people lack adequate control over their own constitutive properties, or what is often called their "constitutive luck" (as opposed to causal luck).[25]

Libertarianism

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Main article: Libertarianism (metaphysics)

Free-will libertarianism is the view that the free-will thesis (that we, ordinary humans, have free will) is true and that determinism is false; in first-order language, it is the view that we (ordinary humans) have free will and the world does not behave in the way described by determinism.[26][27][28] Libertarianism is one of the popular solutions to the problem of free will, roughly the problem of settling the question of whether we have free will and the logically prior question of what free will amounts to.[29] The main rivals to libertarianism are soft determinism and hard determinism.

Libertarian Robert Kane (editor of the Oxford Handbook of Free Will) is a leading incompatibilist philosopher in favour of free will. Kane seeks to hold persons morally responsible for decisions that involved indeterminism in their process.[30][31][32] Critics maintain that Kane fails to overcome the greatest challenge to such an endeavor: "the argument from luck".[33] Namely, if a critical moral choice is a matter of luck (indeterminate quantum fluctuations), then the question of holding a person responsible for their final action arises. Moreover, even if we imagine that a person can make an act of will ahead of time, to make the moral action more probable in the upcoming critical moment, this act of 'willing' was itself a matter of luck. Kane objects to the validity of the argument from luck because the latter misrepresents the chance as if it is external to the act of choosing.[34]: 247-248  The free will theorem of John H. Conway and Simon B. Kochen further establishes that if we have free will, then quantum particles also possess free will.[35][36] This means that starting from the assumption that humans have free will, it is possible to pinpoint the origin of their free will in the quantum particles that constitute their brain.[37]: 10-11 

Such philosophical stance risks an infinite regress, however;[38][39]: 7  if any such mind is real, an objection can be raised that free will would be impossible if the choosing is shaped merely by luck or chance.[40]: 743-744 

Libertarianism in the philosophy of mind is unrelated to the like-named political philosophy. It suggests that we actually do have free will, that it is incompatible with determinism, and that therefore the future is not determined.

One famous proponent of this view was Lucretius, who asserted that the free will arises[41]: 51  out of the random, chaotic movements of atoms, called "clinamen".[41]: 48-49  One major objection to this view is that science has gradually shown that more and more of the physical world obeys completely deterministic laws, and seems to suggest that our minds are just as much part of the physical world as anything else. If these assumptions are correct, incompatibilist libertarianism can only be maintained as the claim that free will is a supernatural phenomenon, which does not obey the laws of nature (as, for instance, maintained by some religious traditions).

However, many libertarian view points now rely upon an indeterministic view of the physical universe, under the assumption that the idea of a deterministic, clockwork universe has become outdated since the advent of quantum mechanics.[37]: 4  By assuming an indeterministic universe, libertarian philosophical constructs can be proposed under the assumption of physicalism.[42]: 200 

There are libertarian view points based upon indeterminism and physicalism, which is closely related to naturalism.[43] A major problem for naturalistic libertarianism is to explain how indeterminism can be compatible with rationality and with appropriate connections between an individual's beliefs, desires, general character and actions. A variety of naturalistic libertarianism is promoted by Robert Kane,[33][44] who emphasizes that if our character is formed indeterministically (in "self-forming actions"), then our actions can still flow from our character, and yet still be incompatibilistically free.

Alternatively, libertarian view points based upon indeterminism have been proposed without the assumption of naturalism. At the time C. S. Lewis wrote Miracles,[45] quantum mechanics (and physical indeterminism) was only in the initial stages of acceptance, but still Lewis 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 (noting that, under a physicalist point of view, the non-physical entity must be independent of the self-identity or mental processing of the sentient being). Lewis mentions this only in passing, making clear that his thesis does not depend on it in any way.

Others may use some form of Donald Davidson's anomalous monism to suggest that although the mind is in fact part of the physical world, it involves a different level of description of the same facts, so that although there are deterministic laws under the physical description, there are no such laws under the mental description, and thus our actions are free and not determined.

Hard determinism

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Main article: Hard determinism
Schopenhauer said "Man is free to do what he wills, but he cannot will what he wills." The hard determinist says then, there is no "free will".

Those who reject free will and accept determinism are variously known as "hard determinists", hard incompatibilists, free will skeptics, free will illusionists, or impossibilists. They believe that there is no free will and that any sense of the contrary is an illusion.[46] Hard determinists do not deny that one has desires, but say that these desires are causally determined by an unbroken chain of prior occurrences. According to this philosophy, no wholly random, spontaneous, mysterious, or miraculous events occur. Determinists sometimes assert that it is stubborn to resist scientifically motivated determinism on purely intuitive grounds about one's own sense of freedom. They reason that the history of the development of science suggests that determinism is the logical method in which reality works.

William James said that philosophers (and scientists) have an "antipathy to chance".[47]: 153  Absolute chance, a possible implication of quantum mechanics and the indeterminacy principle, supports the existence of indefinite causal structures.[48]

Moral implications

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Since many believe that free will is necessary for moral responsibility, hard determinism may imply disastrous consequences for their theory of ethics, resulting in a domino theory of moral nonresponsibility.[49][50]

As something of a solution to this predicament, one might embrace the so-called illusion of free will. This thesis argues in favor of maintaining the prevailing belief in free will for the sake of preserving moral responsibility and the concept of ethics.[51] However, critics argue that this move renders morality merely another "illusion", or else that this move is simply hypocritical.

The determinist will add that, even if denying free will does mean morality is incoherent, such a result has no effect on the truth. However, hard determinists often have some sort of moral system that relies explicitly on determinism. A determinist's moral system simply bears in mind that every person's actions in a given situation are, in theory, predicted by the interplay of environment and upbringing.

Hard incompatibilism

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Hard incompatibilism, like hard determinism, is a type of skepticism about free will. Hard incompatibilism is a term coined by Derk Pereboom to designate the view that both determinism and indeterminism are incompatible with having free will and moral responsibility.[52] Like the hard determinist, the hard incompatibilist holds that if determinism were true, people would not have free will. But Pereboom argues in addition that if decisions were indeterministic events, free will would also be precluded. In his view, free will is the control in action required for the desert aspect of moral responsibility—for people to deserve to be blamed or punished for immoral actions, and to be praised or rewarded for morally exemplary actions. He contends that if people's decisions were indeterministic events, their occurrence would not be in the control of the agent in the way required for such attributions of desert.[53] The possibility for free will that remains is libertarian agent causation, according to which agents as substances (thus not merely as having a role in events) can cause actions without being causally determined to do so. Pereboom argues that for empirical reasons it is unlikely that people are agent causes of this sort, and that as a result, it is likely that they lack free will.[54]

Experimental research

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In recent years researchers in the field of experimental philosophy have been working on determining whether ordinary people, who are not experts in this field, naturally have compatibilist or incompatibilist intuitions about determinism and moral responsibility.[55] Some experimental work has even conducted cross-cultural studies.[56] The debate about whether people naturally have compatibilist or incompatibilist intuitions has not come out overwhelmingly in favor of one view or the other. Still, there has been some evidence that people can naturally hold both views. For instance, when people are presented with abstract cases which ask if a person could be morally responsible for an immoral act when they could not have done otherwise, people tend to say no, or give incompatibilist answers, but when presented with a specific immoral act that a specific person committed, people tend to say that that person is morally responsible for their actions, even if they were determined (that is, people also give compatibilist answers).[57]

See also

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References

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Incompatibilism

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Incompatibilism is the philosophical thesis that free will—the capacity of agents to make choices that are not fully determined by prior causes and natural laws—is logically incompatible with determinism, the doctrine that every event, including human actions, is causally necessitated by preceding events and the laws of nature.[1] This position holds that the two cannot coexist: if determinism is true, free will is impossible, and if free will exists, determinism must be false.[2] The term "incompatibilism" was coined in the early 1960s as part of the analytic tradition in philosophy of action, marking a key distinction from compatibilism, which argues that free will can be reconciled with determinism.[1] Incompatibilism encompasses several variants, each addressing the implications of this incompatibility for human agency and moral responsibility. Classical incompatibilism, often linked to the "leeway" condition, emphasizes that free will requires the ability to do otherwise in the actual sequence of events, which determinism precludes by fixing outcomes based on prior states.[1] Source incompatibilism, in contrast, focuses on the requirement that agents serve as the ultimate source or originator of their actions, arguing that determinism undermines this by tracing causation back to factors beyond the agent's control, such as the distant past.[2] These views underpin broader positions within incompatibilism: hard determinism accepts determinism as true and thus denies free will; libertarianism affirms free will and rejects determinism in favor of indeterminism or agent causation; and hard incompatibilism, as defended by philosophers like Derk Pereboom,[3] maintains that free will is unattainable whether determinism holds or not, due to unavoidable luck or causal chains.[4] Central arguments for incompatibilism include the Consequence Argument, which posits that agents have no choice about the past or the laws of nature, and since determinism implies that the future is a consequence of these, agents lack choice over their actions.[4] This debate has profound implications for ethics, law, and psychology, influencing discussions on moral responsibility, punishment, and even empirical studies of folk intuitions about free will.[1] Despite challenges from compatibilists who redefine free will in terms of uncoerced action or reasons-responsiveness, incompatibilism remains a dominant framework in contemporary philosophy of mind and action.[2]

Fundamentals

Definition and Core Thesis

Incompatibilism is the philosophical position that free will is logically incompatible with determinism, maintaining that the truth of determinism would preclude the existence of free will.[5][6] At its core, this thesis posits that free will necessitates the ability to do otherwise—known as alternative possibilities—whereby an agent could have performed a different action under identical circumstances.[7] Determinism, by contrast, asserts that every event, including human actions, is causally necessitated by prior states of the universe and the laws of nature, leaving no room for genuine alternatives.[8] Thus, incompatibilism argues that since determinism eliminates alternative possibilities, it eliminates free will as well.[5] The logical structure of incompatibilism can be expressed simply: if determinism (denoted as $ D $) is true, and free will requires indeterminism (denoted as $ \neg D $), then $ D $ entails the negation of free will ($ D \rightarrow \neg FW $).[9] Incompatibilists contend that this entailment holds because deterministic causation renders all outcomes inevitable, undermining the control required for free will.[5] This stance sharply distinguishes incompatibilism from compatibilism, which redefines free will in ways compatible with determinism, such as the absence of external constraints or alignment with one's desires.[10] Incompatibilists, however, reject such redefinitions, insisting on a robust, libertarian conception of free will that demands true alternative possibilities and ultimate sourcehood of actions.[6] The term "incompatibilism" was coined in the early 1960s within analytic philosophy to denote this opposition to compatibilist reconciliations of free will and determinism. Varieties of incompatibilism include libertarianism, which affirms both free will and the falsity of determinism as a response to this incompatibility.[5]

Key Concepts: Free Will and Determinism

Determinism is the philosophical thesis that every event, including human actions, is causally necessitated by prior events and the laws of nature, leaving no room for alternative outcomes given the same initial conditions.[8] This view posits a complete chain of causation extending backward indefinitely, such that the state of the universe at any future time is fully determined by its past state and unchanging natural laws. A formal statement of this thesis, often attributed to classical physics but applicable more broadly, is: for any time $ t > t_0 $, the state of the universe at $ t $ is logically entailed by its state at $ t_0 $ together with the laws of nature.[8] Philosophers distinguish several types of determinism, though causal determinism—grounded in physical laws and antecedent conditions—remains central to debates about human agency.[8] Logical determinism asserts that all truths about the future are already fixed by the logical structure of past and present truths, as in the case of propositions that must be true or false eternally. Theological determinism, by contrast, holds that every event is predetermined by divine will or foreknowledge, rendering outcomes inevitable from God's perspective.[11] While these variants share the idea of fixity, causal determinism predominates in incompatibilist discussions due to its alignment with scientific worldviews. Free will refers to the capacity of rational agents to control their actions in a way that originates from themselves, typically requiring either alternative possibilities or ultimate sourcehood.[6] The alternative possibilities condition emphasizes the ability to do otherwise in identical circumstances, meaning an agent could have chosen a different action without changing external factors.[6] Sourcehood, meanwhile, demands that the agent serve as the ultimate originator of their actions, uncaused by prior events in a way that traces back entirely to the agent's own constitution.[6] A common misconception equates free will with mere randomness or unpredictability, but it instead involves controlled, non-determined agency where the agent exercises genuine authorship over choices.[6] These concepts of determinism and free will underpin the incompatibilist position that they cannot coexist.[9]

Historical Origins

Ancient and Medieval Roots

In ancient Greek philosophy, the Stoics, particularly Chrysippus, developed a view of fate as a deterministic chain of causes that encompassed all events, yet they maintained its compatibility with voluntary action through the concept of assent, where individuals freely endorse impressions leading to choices.[12] This compatibilist stance contrasted sharply with the Epicureans, who introduced the atomic swerve—a spontaneous, indeterministic deviation in the motion of atoms—to break the bonds of rigid determinism and preserve human free will against fatalistic necessity.[13] Aristotle, in his Nicomachean Ethics, laid proto-incompatibilist groundwork by defining voluntary action as originating from the agent without external compulsion or ignorance, implying a form of agency that resists full causal predetermination and underpins moral responsibility.[14] Medieval thought deepened these tensions through theological lenses, particularly in Christian and Islamic philosophy. Augustine grappled with divine foreknowledge and human freedom in works like De libero arbitrio, arguing that God's eternal knowledge does not negate voluntary choice but creates an apparent incompatibility, as foreknowledge seems to fix future actions while moral accountability demands alternative possibilities.[15] In Islamic philosophy, Avicenna (Ibn Sina) reconciled necessity with choice by positing that human actions arise from the soul's rational deliberation within a deterministic cosmic order emanating from the Necessary Existent (God), yet he allowed for a limited indeterminacy in volition to affirm agency.[16] Averroes (Ibn Rushd), building on this, emphasized human responsibility for evil and moral choice against deterministic interpretations of divine causation, viewing free will as essential for ethical judgment despite the necessities of nature.[17] A central incompatibilist worry in these traditions was theological determinism, where God's omniscience implies no genuine alternatives for human actions, undermining the free will required for moral accountability—a dilemma vividly highlighted in Augustine's analysis of grace and sin.[15] Boethius, in The Consolation of Philosophy, attempted to resolve divine foreknowledge through the concept of eternity, where God perceives all time simultaneously without imposing necessity, yet this solution underscored persistent incompatibilist concerns about how timeless knowledge could coexist with temporal human agency.[18]

Modern Developments

The modern development of incompatibilism emerged prominently during the Enlightenment, as philosophers grappled with mechanistic views of the universe and their implications for human agency. René Descartes' substance dualism posited that the mind, as a non-physical thinking substance, interacts with the body in ways that transcend deterministic physical laws, thereby implying an indeterministic element in mind-body causation essential for free will.[19] This interactionist framework allowed Descartes to defend libertarian free will against the rising tide of materialism, though it raised unresolved questions about how immaterial mind could causally influence material body without violating conservation laws.[20] In contrast, Baruch Spinoza advanced a strict deterministic metaphysics in which everything, including human actions, follows necessarily from the eternal nature of God or Nature, rendering free will an illusion born of ignorance of causal necessities.[21] Spinoza argued that the will is not free but determined by external causes, with the apparent freedom arising from our limited understanding of the infinite chain of causes; true freedom, for him, lies in intellectual comprehension of this necessity rather than contracausal choice. Paul-Henri Thiry, Baron d'Holbach, extended this deterministic outlook in his 1770 work Système de la nature, asserting a materialist hard determinism where all events, including volitions, form an unbreakable chain of causes and effects governed by natural laws, leaving no room for free will or moral autonomy.[22] Holbach's polemical rejection of supernatural interventions emphasized that human actions are as inevitably determined as physical motions, critiquing illusions of liberty as products of theological error.[23] The 19th century saw incompatibilist themes infused with pessimism and cultural critique. Arthur Schopenhauer, building on Kantian influences, identified the world as driven by a blind, insatiable Will—the thing-in-itself—that manifests as determined striving in phenomena, rendering free will illusory since actions stem from this underlying necessity rather than rational choice.[24] His pessimistic philosophy portrayed human existence as a cycle of unfulfilled desires compelled by this Will, with ethical salvation possible only through its denial, not through libertarian agency.[25] Friedrich Nietzsche mounted a radical critique of free will as a metaphysical error rooted in erroneous notions of causa sui (self-causation), dismissing it as a Christian invention that falsifies the natural world's flux of drives and instincts.[26] While rejecting metaphysical libertarianism, Nietzsche exhibited compatibilist leanings by revaluing agency in terms of psychological strength and self-overcoming within a deterministic framework, though he ultimately undermined traditional responsibility doctrines tied to free will.[27] By the early 20th century, incompatibilism transitioned into analytic philosophy through G.E. Moore's 1912 paper "Free Will," which clarified the distinction between determinism— the thesis that all events have sufficient prior causes—and fatalism, the erroneous belief in inevitable outcomes regardless of causes, thereby paving the way for explicit debates on whether determinism precludes moral responsibility.[28] Moore's analysis refuted simplistic conflations that had muddled prior discussions, emphasizing that incompatibilists could coherently argue for free will's dependence on indeterminism without endorsing fatalistic resignation. This work marked a shift toward rigorous logical examination, influencing subsequent analytic treatments of the free will problem.

Main Arguments for Incompatibilism

Consequence Argument

The Consequence Argument constitutes a primary logical proof for incompatibilism, contending that determinism precludes agents from having the power to do otherwise with respect to their actions. Its origins trace to G. E. Moore's 1912 discussion in Ethics, where he anticipated key elements by arguing that free will requires the ability to act contrary to what determinism would necessitate, and was formally developed by Peter van Inwagen in his 1975 paper "The Incompatibility of Free Will and Determinism" and elaborated in his 1983 book An Essay on Free Will.[29][9] Van Inwagen's formal structure employs the modal operator Np\mathbf{N}p, defined as "pp and no one has, or ever had, any choice about whether pp." The argument relies on two inference rules: Alpha, which states that if □p\Box p (necessarily pp), then Np\mathbf{N}p; and Beta, the principle that if Np\mathbf{N}p and N(p⊃q)\mathbf{N}(p \supset q), then Nq\mathbf{N}q. Let P0P_0 denote the complete state of the universe at a time before any agents existed, and let LL be the conjunction of all laws of nature. Under determinism, for any true proposition PP about a present action, □((P0∧L)⊃P)\Box ((P_0 \land L) \supset P). Applying Alpha yields N((P0∧L)⊃P)\mathbf{N}((P_0 \land L) \supset P). Given the intuitive premises NP0\mathbf{N}P_0 (no one has choice about the fixed past) and NL\mathbf{N}L (no one has choice about the laws), Beta transfers the lack of choice stepwise to infer NP\mathbf{N}P. Thus, no one has choice about their present actions, rendering free will impossible under determinism.[9][29] A key premise underlying Beta is the fixity of the laws of nature, encapsulated in van Inwagen's assertion: "No one has, or ever had, any choice about whether the laws of nature obtain." This principle underscores the argument's reliance on the intuitive idea that agents cannot alter fundamental necessities beyond their control. Critics often target Beta's validity, but proponents maintain it captures commonsense intuitions about consequence and inability.[9] The argument has notable variants. The counterfactual version, advanced by David Lewis in 1981, reformulates it to emphasize alternative possibilities: if determinism holds, then for an agent to have done otherwise, either the past or the laws would have differed, requiring implausible "incredible" abilities like rendering the past false while holding it fixed. The dialectical version, also from van Inwagen, shifts focus to debate compatibilist analyses of "can" or "ability to do otherwise," pressing opponents to explain how such abilities remain under deterministic constraints without violating the fixity of past and laws. While the Consequence Argument centers on logical transfer of inability, it intersects briefly with sourcehood concerns regarding agents as ultimate origins of action.[9]

Manipulation and Sourcehood Arguments

Manipulation arguments for incompatibilism contend that if an agent's actions are causally determined by factors beyond their control, similar to cases of direct manipulation, then the agent lacks the kind of control required for free will and moral responsibility. These arguments typically proceed in two steps: first, establishing that manipulated agents intuitively lack responsibility; second, drawing a parallel between manipulation and determinism, where past events and laws of nature determine actions in an analogous way. A prominent example is Alfred R. Mele's Zygote Argument (2006), featuring Ernie, an agent whose zygote is created by neuroscientists in a deterministic universe to ensure that Ernie will perform a specific action, such as killing someone, thirty years later.[30] Intuitively, Ernie is not morally responsible for the killing because his constitution and subsequent mental development are determined by the manipulators' design, bypassing his ability to be the ultimate source of his action. Derk Pereboom (2001) develops a related four-case argument, starting with a case of overt neural manipulation by a neuroscientist that determines an agent's decision to kill, where the agent is clearly not responsible. He then presents three further cases with progressively less direct intervention—mid-life reprogramming, neurophysiological alteration from birth, and finally determinism itself—arguing that no relevant difference emerges across the cases to restore responsibility in the deterministic scenario.[30] Sourcehood arguments complement manipulation cases by emphasizing that free will requires the agent to be the ultimate or originating source of their actions, which determinism precludes by tracing all actions back to prior non-agent causes. Roderick Chisholm articulates this in terms of agent causation, where true freedom demands that the agent, rather than events, initiates the causal chain without being determined by it. Galen Strawson develops the requirement further, arguing that moral responsibility and free will necessitate "ultimate responsibility," meaning the agent must be the uncaused cause of their character and choices; however, under determinism, this traces infinitely back to factors outside the agent's control, rendering sourcehood impossible. Thus, deterministic chains undermine the agent's status as the ultimate source, just as manipulation does. Intuition pumps reinforce these arguments by highlighting the causal origins of actions. The "garden of forking paths" metaphor illustrates determinism as a single, unbranching path through time, where no genuine choices or alternative possibilities exist for the agent, unlike an indeterministic "garden" with multiple routes symbolizing freedom.[31] Similarly, design arguments portray the universe as a pre-programmed machine, akin to a clockwork device engineered by natural laws or a divine creator, where agents are mere components unable to originate actions independently of the design. Frankfurt-style counterexamples, which aim to show that moral responsibility does not require alternate possibilities, fail to undermine sourcehood arguments because even if the ability to do otherwise is absent, the requirement for the agent to be the ultimate source of the actual action remains intact. Incompatibilists maintain that manipulated or determined agents, like those in the Ernie case, lack this sourcehood regardless of whether counterfactual interveners would have ensured the outcome.

Varieties of Incompatibilism

Libertarianism

Libertarianism represents a form of incompatibilism that denies the truth of determinism while affirming the existence of free will, positing that genuine alternatives for action are possible only through indeterminism in the causal processes leading to decisions. This view maintains that free will requires the falsity of determinism (¬D) to allow agents the ability to do otherwise in a robust, alternative-possibilities sense, thereby enabling moral responsibility without reliance on deterministic causation.[32] Libertarian theories divide into two primary varieties: agent-causal and event-causal accounts. In agent-causal libertarianism, the agent, as a non-physical or irreducible substance, directly initiates actions in a non-deterministic manner, uncaused by prior events yet guided by reasons; this approach traces back to Roderick Chisholm's defense of the agent as a "prime mover unmoved" and is elaborated in Timothy O'Connor's metaphysics of agent causation, where the agent's causal power is fundamental and not reducible to event-based processes.[33] By contrast, event-causal libertarianism locates indeterminism within the chain of events preceding action, often invoking quantum-level randomness at key decision points to break deterministic chains; Robert Kane's influential model emphasizes "self-forming actions" (SFAs), indeterministic choices during moral dilemmas that establish ultimate responsibility by shaping the agent's character over time.[34] A central challenge to libertarianism is the "luck objection," which contends that introducing indeterminism merely replaces deterministic necessity with randomness, thereby undermining the agent's control over outcomes and rendering free actions a matter of chance rather than rational agency. This critique, prominently articulated by Peter van Inwagen, argues that without determinism, agents cannot be the ultimate sources of their actions, as indeterministic processes would make results arbitrary.[35] In response, proponents like Kane develop the concept of "plural voluntary control," whereby indeterminism in self-forming actions amplifies into agent-directed rational deliberation, allowing the agent to exert effortful control over multiple viable options despite the absence of determining causes, thus preserving intentionality and responsibility.[34]

Hard Determinism

Hard determinism represents a strand of incompatibilism that affirms the truth of determinism while rejecting the possibility of free will. Under this view, determinism (D) entails that every event, including human actions, is causally necessitated by prior states of the universe and the laws of nature, rendering alternative possibilities impossible and thus negating free will (¬free will). Actions are fully determined by chains of causes stretching back indefinitely, leaving no room for libertarian notions of agent causation or indeterministic choice.[36] This position traces its roots to Enlightenment thinkers who integrated materialist philosophy with emerging scientific understandings of causality. Baron d'Holbach, in his 1770 treatise Système de la Nature, advanced a materialist hard determinism, arguing that humans, as part of the physical world, are governed entirely by mechanical laws and external impulses, with the will itself being a product of necessity rather than an autonomous force. Complementing this, Pierre-Simon Laplace's 1814 A Philosophical Essay on Probabilities introduced the famous thought experiment of an "intellect" (later termed Laplace's demon) that, with complete knowledge of all particles' positions and velocities at any moment, could predict the entire future trajectory of the universe, underscoring the deterministic predictability of all events including human behavior.[23][37] Regarding implications for human agency, hard determinists contend that the subjective experience of choice is illusory, arising from ignorance of the causal chains that dictate behavior, and that compatibilist conceptions of free will—often defined as acting without external coercion—are a misnomer, as they conflate mere behavioral regularity with genuine autonomy in a determined world. In contrast to libertarianism, which denies determinism to preserve free will, hard determinism accepts D as empirically supported by science and philosophy.[38] Contemporary variants of hard determinism draw on neuroscientific findings to bolster the deterministic rejection of free will. For instance, some proponents invoke Benjamin Libet's 1983 experiments, which demonstrated that brain activity preceding conscious awareness of a decision to act (readiness potential) suggests unconscious neural processes initiate voluntary actions, aligning with a view that conscious choice is epiphenomenal rather than originary. These interpretations reinforce the hard determinist thesis by portraying agency as a retrospective illusion in a causally closed physical system.[39][40]

Hard Incompatibilism and Impossibilism

Hard incompatibilism posits that free will is incompatible with both determinism and indeterminism, maintaining agnosticism about whether the universe is deterministic while arguing that moral responsibility is impossible in either case. According to this view, under determinism, agents lack the ultimate sourcehood required for free will because their actions are ultimately caused by factors beyond their control; conversely, indeterminism introduces randomness that undermines agency rather than enhancing it, as chance events do not confer genuine control over one's choices. Derk Pereboom introduced this position in his 1995 paper "Determinism al Dente," where he argued that neither deterministic causation nor libertarian indeterminism suffices for the kind of alternative possibilities or sourcehood needed for moral responsibility. He further developed the view in his 2001 book Living Without Free Will, emphasizing that free will requires an agent's actions to originate from her without being determined by prior causes outside her control, a condition unmet in both scenarios. A key argument for hard incompatibilism is Pereboom's four-case argument, which extends manipulation cases to show the failure of sourcehood under indeterminism as well. In the first case, an agent is directly manipulated by neuroscientists to perform an action; in the second, the manipulation occurs through earlier life programming; the third involves divine pre-programming at birth; and the fourth posits intrinsic indeterminism in the brain without external intervention. Intuitively, the agent lacks responsibility in the first three cases due to manipulation, and Pereboom contends that the fourth case fares no better, as quantum indeterminacy merely replaces manipulation with chance, neither providing true control. John Martin Fischer has offered a variant interpretation in his 1994 work The Metaphysics of Free Will, suggesting that while full control might be impossible, a form of "guidance control" could mitigate some concerns, though this does not resolve the deeper incompatibilist worry about ultimate sourcehood. Impossibilism represents a stronger form of hard incompatibilism, asserting that free will is impossible regardless of the truth of determinism, due to an unavoidable infinite regress in the requirement for self-determination. Galen Strawson articulates this in his 2011 chapter "The Impossibility of Ultimate Responsibility?", arguing that true moral responsibility demands that agents be the ultimate source of their actions, which requires self-creating one's character and motives ex nihilo—an impossibility that leads to an infinite regress of prior causes or decisions. Under this view, both deterministic and indeterministic worlds fail to provide the "ultimate responsibility" needed, as indeterminism offers only luck, not agency, reinforcing the basic argument that no finite being can originate itself sufficiently for free will.[41] In response to challenges from libertarianism, which proposes agent-causation as a solution to the regress by positing non-physical causation by the agent, hard incompatibilists like Pereboom maintain that such causation lacks empirical support and still begs the question of the agent's own origination. Recent developments in hard incompatibilism include nuanced proposals for practical implications, such as Pereboom's advocacy for "hard-line" replies to moral responsibility skepticism, which reject retributive punishment in favor of consequentialist alternatives like quarantine and rehabilitation to protect society without assuming desert-based blame. These approaches emphasize that rejecting free will does not undermine ethics or meaning but invites forward-looking strategies for human flourishing.[42]

Implications and Applications

Moral Responsibility

Incompatibilism challenges traditional conceptions of moral responsibility by asserting that genuine responsibility requires free will, which is incompatible with determinism. Specifically, moral responsibility demands either the principle of alternative possibilities—where agents could have done otherwise in the same circumstances—or sourcehood, whereby agents are the ultimate originators of their actions. Under determinism, however, every event, including human actions, is causally necessitated by prior states of the universe, eliminating genuine alternatives and rendering agents mere conduits for causal chains rather than ultimate authors.[9][7] This leads to the core incompatibilist argument against desert-based moral responsibility: if actions are fully determined, agents cannot be held truly blameworthy or praiseworthy, as they lack the control required for retributive desert. Incompatibilists critique P. F. Strawson's compatibilist defense of reactive attitudes—such as resentment toward wrongdoing and gratitude for beneficence—as natural responses that underpin moral practices independent of metaphysical determinism. They contend that these attitudes implicitly presuppose indeterminism or sourcehood for their justification, and that recognizing determinism would rationally undermine them, replacing intuitive blame with a more detached, objective stance.[43][44] Libertarians, as a variety of incompatibilists, seek to preserve moral responsibility by endorsing indeterminism, arguing that non-deterministic processes—such as quantum indeterminacy in the brain—enable agents to initiate action sequences that ground alternative possibilities and ultimate sourcehood. In Robert Kane's influential event-causal libertarianism, for instance, free will emerges in "self-forming actions" where indeterministic neural mechanisms allow agents to resolve moral dilemmas, thereby securing the control needed for desert-entailing praise and blame.[6] Hard determinists and hard incompatibilists, by contrast, maintain that determinism (or causally irrelevant indeterminism) precludes free will and thus eliminates basic desert, advocating a shift from retributivism—which justifies blame and punishment as payback for wrongdoing—to consequentialist frameworks that emphasize deterrence, rehabilitation, and societal protection. Derk Pereboom's hard incompatibilism exemplifies this stance, arguing that moral responsibility skepticism does not erode ethical life but redirects it toward forward-looking strategies that promote welfare without illusory notions of ultimate authorship.[45][44] A central debate arises over the emotional implications of this skepticism, particularly whether incompatibilism renders attitudes like regret or resentment untenable or irrational. Pereboom counters that such backward-looking emotions can be gradually replaced or reconceptualized as concern for future consequences, preserving interpersonal relationships and moral motivation without presupposing free will.[45]

Legal and Ethical Consequences

Incompatibilist views on free will have significant implications for criminal justice systems, particularly in challenging the retributive model of punishment that assumes moral desert based on autonomous choice. If determinism precludes genuine free will, incompatibilists argue that offenders cannot be deservedly punished for their actions, as these are ultimately caused by factors beyond their control, such as genetic predispositions, environmental influences, and prior causal chains. Instead, legal responses should prioritize forward-looking goals like deterrence, rehabilitation, and public protection to minimize harm without invoking retribution. This perspective was vividly illustrated in Clarence Darrow's 1924 defense of Nathan Leopold and Richard Loeb, where he invoked deterministic principles to argue that the defendants' criminal act was the inevitable product of heredity and environment, pleading for life sentences focused on reform rather than execution.[46] Modern incompatibilists, such as Derk Pereboom and Gregg D. Caruso, extend this logic by proposing a "public health-quarantine model" for criminal justice, treating offenders akin to individuals quarantined for contagious diseases—incapacitated for societal safety but without retributive intent, emphasizing rehabilitation and reintegration over punitive desert. Ethically, incompatibilism prompts a reevaluation of normative theories, favoring consequentialist frameworks like utilitarianism that assess actions by their outcomes rather than intrinsic moral worth tied to free agency. Under hard incompatibilism, utilitarian approaches remain viable because they justify moral practices based on their utility in promoting overall well-being, independent of assumptions about libertarian free will or basic desert. Pereboom argues that this shift does not undermine ethics entirely, as consequentialist evaluations can still guide right and wrong without requiring ultimate responsibility, allowing for moral education and social norms that enhance human flourishing. In contrast, virtue ethics faces greater strain, as it traditionally posits that moral character is freely cultivated through deliberate choices, a process incompatibilists view as illusory under determinism, potentially reducing virtues to causally determined traits rather than praiseworthy achievements. In policy applications, incompatibilist views align with non-retributive approaches that emphasize forward-looking strategies for addressing criminal behavior and promoting societal welfare. A key challenge for incompatibilism in legal and ethical domains is reconciling its logical exemption from retributive responsibility with entrenched public intuitions that demand blame and punishment for moral wrongs. Pereboom's exemptionist framework addresses this by advocating "guidance control" mechanisms—forward-looking attitudes like moral protest and inducement—that preserve social order without basic desert, though critics argue this may erode deterrence if not balanced with intuitive notions of accountability. This tension underscores ongoing reforms in jurisdictions experimenting with reduced sentencing disparities, highlighting incompatibilism's potential to humanize justice systems while navigating cultural resistance to determinism.

Contemporary Perspectives

Experimental Philosophy and Neuroscience

Experimental philosophy has investigated folk intuitions regarding free will and determinism, revealing patterns that often align with incompatibilist views in specific contexts. In studies by Nahmias and colleagues, participants exposed to abstract descriptions of a deterministic universe tended to judge agents as possessing free will and moral responsibility, suggesting compatibilist leanings.[47] However, when presented with concrete scenarios involving neuroscientific determinism—such as brain processes mechanistically causing actions—many participants shifted toward incompatibilist judgments, attributing reduced responsibility to the agents.[47] This distinction highlights how framing influences intuitions, with abstract determinism appearing less threatening to agency than tangible, causal explanations. Further experimental work by Murray and Nahmias explored the "bypassing" hypothesis, positing that incompatibilist intuitions arise when actions seem to circumvent the agent's conscious deliberation.[48] In their surveys, participants rated agents as lacking free will and responsibility primarily in cases where deterministic influences were perceived to bypass rational self-control, such as in scenarios of neural manipulation or unconscious causation.[48] Conversely, when determinism was described as operating through the agent's own reasons and desires without bypassing, compatibilist attributions of responsibility prevailed.[48] These findings support an error theory for apparent incompatibilism, suggesting that folk judgments target the absence of agent-involving mechanisms rather than determinism per se. Neuroscience has provided empirical challenges to libertarian notions of free will through studies on the timing of conscious decisions. Libet's seminal 1983 experiments measured the readiness potential (RP), a buildup of electrical activity in the brain preceding voluntary movements, finding it onset approximately 350 milliseconds before participants reported conscious awareness of their intention to act.[49] This suggested that unconscious neural processes initiate actions prior to conscious will, raising questions about the causal role of conscious decisions in incompatibilist frameworks. Building on this, Soon et al.'s 2008 fMRI study extended the temporal gap, decoding participants' choices to press one of two buttons up to 7-10 seconds before conscious awareness, with predictive signals emerging in frontopolar cortex and parietal regions.[50] Such results imply that high-level decisions may be determined by preceding brain activity, potentially undermining sourcehood accounts central to libertarian incompatibilism. Recent replications and critiques in the 2020s have nuanced these findings, questioning their implications for determinism. Schurger et al.'s 2012 accumulator model reinterpreted the RP not as evidence of unconscious initiation but as arising from stochastic fluctuations in neural activity that reach a threshold for movement, aligning with Libet's behavioral timings without presupposing predetermination.[51] This perspective shifts emphasis from fixed causal chains to probabilistic processes, offering a compatibilist-friendly resolution while highlighting methodological limitations in earlier studies. These empirical insights lend support to manipulation-style arguments in incompatibilism by illustrating how unconscious or pre-conscious influences might bypass agent control, yet they do not conclusively establish determinism, as debates persist over whether neural timing disproves libertarian freedom or merely reveals the integration of conscious veto powers within broader decision-making.[51]

Criticisms and Debates

Compatibilists have mounted significant challenges to incompatibilist claims, particularly by questioning the necessity of alternative possibilities for moral responsibility. In his seminal 1969 paper, Harry Frankfurt introduced counterfactual scenarios—now known as Frankfurt-style cases—where an agent performs an action without the genuine ability to do otherwise, due to a hidden intervener who would compel the outcome if deviation occurred, yet the agent remains fully responsible, undermining the principle that responsibility requires alternate possibilities. Building on this, Frankfurt's 1971 hierarchical theory posits that free will arises from the identification of first-order desires with second-order volitions, allowing agents to act freely even in a deterministic world by aligning lower desires with higher reflective endorsements, thus redefining freedom without reliance on indeterminism.[52] Libertarian forms of incompatibilism, which affirm both indeterminism and free will, encounter internal objections centered on the tension between control and luck. Peter van Inwagen's 2000 rollback argument illustrates this by imagining the universe rewound to a decision point multiple times; if the outcome varies due to indeterminism, the agent's choice appears arbitrary and lucky rather than controlled, suggesting that libertarian freedom cannot escape chance-based explanations.[53] Alfred Mele (2006) amplifies this critique, contending that libertarian mechanisms introducing indeterminism to ensure alternative possibilities inevitably inject present or exploratory luck into decisions, leaving unresolved how agents secure the robust control required for moral responsibility. Contemporary debates within incompatibilism extend to the efficacy of quantum indeterminism and the viability of impossibilism. Christian List (2019) argues that while quantum mechanics introduces micro-level indeterminism, free will operates at the macroscopic psychological level, where effective determinism prevails, rendering quantum effects irrelevant to agential control and alternative possibilities.[54] On impossibilism—the view that free will is impossible irrespective of determinism due to an unavoidable regress in self-determination—critics maintain that the regress is overstated; agent-causal libertarianism, for instance, posits uncaused causal events by the agent as a non-regressive foundation for freedom, avoiding infinite chains while preserving incompatibilist commitments.[55] Incompatibilism's discourse also reveals notable gaps, such as the underrepresentation of non-Western perspectives, where empirical studies indicate that cultural contexts like East Asian traditions yield folk intuitions less aligned with strict incompatibilism, favoring holistic or relational views of agency over individualistic indeterminism.[56] Post-2020 discussions further highlight evolving implications from artificial intelligence, where deterministic algorithms in machine learning systems simulate human-like decisions, intensifying debates on whether such models undermine incompatibilist accounts of human freedom or necessitate reevaluating determinism's scope in hybrid human-AI contexts.[57]

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