What Is the Principle of Alternate Possibilities? Frankfurt's Challenge

Direct Answer

The principle of alternate possibilities (PAP) holds that an agent is morally responsible for an action only if she could have done otherwise. On this view, responsibility presupposes a genuine open alternative: if your past and the laws of nature made your action unavoidable, you are not answerable for it. PAP has been the pivot of the free will debate because it connects the metaphysics of determinism to the ethics of blame.

In 1969, Harry Frankfurt published "Alternate Possibilities and Moral Responsibility," an article that changed the debate. He constructed cases — now called Frankfurt cases — in which an agent could not have done otherwise and yet is plainly responsible. If PAP is false, then the incompatibilist's neat inference from determinism to the absence of responsibility breaks down, and compatibilists gain a powerful tool. The debate over PAP has continued for half a century, and its outcome shapes every contemporary theory of moral responsibility.

Historical Context

The intuition behind PAP is ancient. Aristotle's account of the voluntary links praise and blame to action that is "up to us," and the scholastic tradition sharpened this into the requirement that the will choose among alternatives. In the early modern period, Hume argued that responsibility tracks character and "the power of doing or forbearing," which he read compatibilistically — action according to one's own motives without coercion. The libertarian tradition, from Reid to Kant, made the power of contrary choice central to freedom.

Frankfurt's 1969 paper targeted the assumption that had underwritten both sides of the debate: that responsibility requires alternatives. His counterexamples are disarmingly simple. Suppose Jones would decide to shoot Smith for his own reasons, but a neurosurgeon stands ready to intervene and force the decision if Jones shows any sign of not choosing it. The surgeon never needs to act: Jones decides on his own. Jones could not have done otherwise — the surgeon guaranteed the outcome — yet we judge Jones fully responsible. If this case works, PAP is false.

Key Concepts

The principle of alternate possibilities (PAP). An agent is morally responsible for an action only if she could have done otherwise.

Frankfurt case. A scenario in which (a) the agent acts on her own reasons, (b) a fail-safe mechanism would have ensured the same outcome had she hesitated, and (c) the mechanism never operates. The case aims to separate responsibility from alternatives.

Local vs. global alternatives. Frankfurt cases remove alternatives at the moment of action (local) while the agent retains the general capacity to choose otherwise in other situations (global). Whether global alternatives matter is a live question.

Sourcehood. The view that responsibility depends on whether the action flows from the agent's own reasons, character, and deliberation — its source — rather than on the existence of alternatives.

Reasons-responsiveness. Fischer and Ravizza's development of the idea: an agent is responsible when her action is guided by a mechanism that is moderately responsive to reasons — she would have responded differently had there been sufficient reason to.

Philosophical Perspectives

Frankfurt's argument divided the field. Many incompatibilists conceded that PAP, as originally stated, is false — but they insisted that this does not help the compatibilist. What matters for responsibility, they argued, is not alternatives at the moment of action but the absence of determination over the whole history of the agent: if determinism is true, the agent is not the ultimate source of her action, and that is what rules out responsibility. This "source incompatibilism" absorbed Frankfurt's lesson while preserving the incompatibilist conclusion.

Fischer and Ravizza built a full compatibilist theory on Frankfurt's foundation. Responsibility, they argue, does not require control over alternatives ("regulative control") but only "guidance control": the action must issue from a mechanism that is the agent's own — moderately reasons-responsive and not manipulated. The agent in the Frankfurt case has guidance control; the patient whose brain is directly hijacked by a scientist does not. This distinction lets compatibilists accept determinism while still marking the difference between free and unfree action.

Libertarians, meanwhile, have responded by refining what alternatives they need. Some now argue that responsibility requires only the general ability to do otherwise across situations, or that libertarian free will matters for what we become over time, not for each isolated act. Others, following Robert Kane, insist that ultimate responsibility — not mere alternatives — is what libertarianism is really about.

Modern Reflection

The PAP debate is no longer merely technical. Experimental philosophers have tested Frankfurt cases on ordinary subjects, finding that many — though not all — people judge the agent responsible despite the absence of alternatives. This matters because the criminal law has traditionally assumed a close link between "could have done otherwise" and blameworthiness, and neuroscience has repeatedly suggested that our choices may be fixed before we are aware of them. If Frankfurt is right, even a fully determined choice can be one for which the agent is responsible — provided it flows from her own reasons-responsive machinery.

The deepest legacy of the debate is a shift in how philosophers think about freedom: away from the question "Could I have done otherwise?" and toward the question "Is this action genuinely mine?" That is the question of sourcehood, and it remains the live center of the contemporary debate.

Related Thinkers

• Hume — responsibility based on character and motives
• Daniel Dennett — compatibilist defender of reasons-responsive freedom
• William James — the moral stakes of an open future
• Kant — autonomy and self-legislation

Related Quotes

• "The principle of alternate possibilities is false: a person may be morally responsible for what he has done even though he could not have done otherwise." — Harry Frankfurt, Alternate Possibilities and Moral Responsibility
• "Men are responsible for their actions in virtue of the motives and character from which they spring." — Hume, A Treatise of Human Nature
• "Freedom is not the absence of causes but the presence of reasons." — paraphrase of Daniel Dennett

Sources

• Moral Responsibility — Stanford Encyclopedia of Philosophy
• Arguments for Incompatibilism — Stanford Encyclopedia of Philosophy
• Frankfurt, Alternate Possibilities and Moral Responsibility — The Journal of Philosophy
• Responsibility and Control — Fischer and Ravizza, Cambridge University Press

Further Learning

• Continue with What Is Free Will? and What Is Moral Responsibility?
• Study the Free Will topic and the Understanding Reality collection
• Read about ethics and the philosophy of action