Frankfurt cases

Frankfurt cases (also known as Frankfurt counterexamples or Frankfurt-style cases) were presented by philosopher Harry Frankfurt in 1969 as counterexamples to the "principle of alternate possibilities", or PAP, which holds that an agent is morally responsible for an action only if that person could have done otherwise.

The principle of alternate possibilities (acronym PAP) forms part of an influential argument for the incompatibility of responsibility and causal determinism, often called the core argument for incompatibilism. This argument is detailed below:

(1) PAP: An agent is responsible for an action only if said agent could have done otherwise.

(2) An agent could have done otherwise only if causal determinism is false.

(3) Therefore, an agent is responsible for an action only if causal determinism is false.

Traditionally, compatibilists (defenders of the compatibility of free will and determinism, like A. J. Ayer, Walter Terence Stace, and Daniel Dennett) reject premise two, arguing that, properly understood, free will is not incompatible with determinism. According to the traditional compatibilist analysis of free will, an agent is free to do otherwise when he would have done otherwise had he wanted to do otherwise. Agents may possess free will, according to the conditional analysis, even if determinism is true.

From the PAP definition "a person is morally responsible for what he has done only if he could have done otherwise", Frankfurt infers that a person is not morally responsible for what he has done if he could not have done otherwise – a point with which he takes issue: our theoretical ability to do otherwise, he says, does not necessarily make it possible for us to do otherwise.

Frankfurt's examples are significant because they suggest an alternative way to defend the compatibility of moral responsibility and determinism, in particular by rejecting the first premise of the argument. According to this view, responsibility is compatible with determinism because responsibility does not require the freedom to do otherwise.

Frankfurt's examples involve agents who are intuitively responsible for their behavior even though they lack the freedom to act otherwise. Here is a typical case:

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