For most of Western history, philosophers assumed that moral responsibility requires free will, and that free will requires the ability to do otherwise. If you couldn't have acted differently — if the outcome was determined in advance — then you aren't responsible for what you did. This seemed obvious. Then, in 1969, a philosopher named Harry Frankfurt published a four-page paper that broke the assumption apart.
The paper was called "Alternate Possibilities and Moral Responsibility," and its argument was built on a single, elegant thought experiment that has been debated in philosophy departments ever since.
The Principle of Alternate Possibilities
The traditional view Frankfurt attacked can be stated simply:
A person is morally responsible for what they have done only if they could have done otherwise.
This is called the Principle of Alternate Possibilities (PAP), and it has deep intuitive appeal. If someone holds a gun to your head and forces you to hand over money, we don't blame you — because you had no real choice. Responsibility, it seems, requires options.
PAP also connects naturally to the free will debate. If determinism is true — if every event, including every human decision, is the inevitable consequence of prior causes — then no one could ever have done otherwise. And if no one could have done otherwise, then by PAP, no one is ever morally responsible for anything. This is the classic incompatibilist argument: determinism and moral responsibility cannot coexist.
Frankfurt thought this argument was wrong. Not because determinism is false, but because PAP itself is false.
The Frankfurt Case
Here is the thought experiment, adapted from Frankfurt's original:
Suppose Jones is deliberating about whether to vote for Candidate A or Candidate B. Unbeknownst to Jones, a neuroscientist named Black has implanted a device in Jones's brain. Black wants Jones to vote for Candidate A. If Jones shows any sign of deciding to vote for Candidate B, Black will activate the device and force Jones to vote for A instead.
As it happens, Jones decides on his own — for his own reasons, through his own deliberation — to vote for Candidate A. Black never activates the device. The device plays no role in Jones's decision.
Now: is Jones morally responsible for voting for Candidate A?
Frankfurt's answer is yes. Jones made the choice himself, for his own reasons, through his own deliberative process. The fact that he couldn't have done otherwise — because Black would have intervened — doesn't diminish his responsibility. He acted on his own will. The alternative was blocked, but it was an alternative he never tried to take.
If this is right, then PAP is false. A person can be morally responsible for an action even when they could not have done otherwise. And if PAP is false, then determinism is no longer a threat to moral responsibility — at least not through this argument.
Why This Matters
The Frankfurt cases didn't settle the free will debate, but they changed its terms fundamentally. Before Frankfurt, the debate was structured around whether we have alternate possibilities. After Frankfurt, the debate shifted to a different question: what kind of relationship between an agent and their action is required for moral responsibility?
Frankfurt's own answer, developed in later work, was that what matters is not whether you could have done otherwise but whether your action flows from the will you want to have. He introduced a distinction between first-order desires (I want to eat the cake) and second-order desires (I want to want to eat healthily). A person acts freely, Frankfurt argued, when their first-order desires align with their second-order desires — when they endorse their own motivations. He called this acting with a wholehearted will.
This is a version of compatibilism — the view that free will and determinism can coexist — but it's a distinctive one. Freedom, for Frankfurt, isn't about having options. It's about being the kind of agent whose actions express their deepest commitments.
The Objections
Frankfurt cases have generated an enormous literature, and the objections are formidable.
The flicker of freedom objection. Some philosophers, notably David Widerker and Robert Kane, have argued that in Frankfurt-style cases, there is still a tiny alternate possibility: Jones could have shown a sign of deciding differently, which would have triggered Black's intervention. The alternate isn't voting for B, but the initial inclination toward B. Frankfurt's defenders respond that this "flicker" of freedom is too thin to ground moral responsibility — if PAP can only be saved by pointing to microscopic mental events, it has lost its intuitive force.
The dilemma objection. Widerker also raised a sharper challenge: in order for the case to work, Jones's decision must be undetermined at the moment Black would need to intervene (otherwise, Black could predict it without a device). But if Jones's decision is undetermined, then we can't say he "would have" decided to vote for A without the device. The counterfactual becomes unclear. This objection has been extensively debated, with philosophers like David Hunt and Alfred Mele proposing refined versions of Frankfurt cases designed to avoid the dilemma.
The moral of the story. Even those who accept Frankfurt's conclusion disagree about what it means. Some see it as a victory for compatibilism. Others — like philosopher Derk Pereboom — accept that PAP is false but argue that moral responsibility is still threatened by determinism through other arguments, particularly the claim that deterministic agents are ultimately products of factors beyond their control.
Frankfurt Beyond Free Will
Frankfurt's influence extends beyond the free will debate. His later work — especially his 1988 book The Importance of What We Care About and his 2004 book The Reasons of Love — explored questions about love, caring, and practical identity. He argued that what gives a human life structure and meaning is not rational deliberation alone but the things we care about — the commitments that define who we are.
Love, in Frankfurt's view, is not an emotion. It is a volitional structure: to love something is to care about it in a way that constrains your will. A parent who loves their child doesn't choose to prioritize the child after weighing costs and benefits. The love itself shapes what counts as a reason. In this sense, love is not a response to value — it is a source of value.
This idea connects back to his work on free will. For Frankfurt, the deepest form of freedom is not having many options. It is wholeheartedness — the state of being undivided in your commitments, of wanting what you want to want, of acting from a will you fully endorse.
The Lasting Question
Frankfurt's four-page paper in 1969 didn't end the debate about free will and responsibility. But it permanently changed the question. Before Frankfurt, philosophers asked: "Can you do otherwise?" After Frankfurt, the deeper question became: "Is the action really yours?"
That question — what it means for an action to be truly your own — turns out to be far harder and far more interesting than the question it replaced. And it's a question that matters well beyond philosophy seminar rooms. Every time we praise, blame, punish, or forgive, we are implicitly making a judgment about whether someone's action was really theirs.
Frankfurt showed us that the answer doesn't depend on alternate possibilities. It depends on something harder to define — and closer to the heart of what it means to be a person.
