Everything so far has assumed that being responsible for an action requires having been able to do otherwise, and in 1969 Harry Frankfurt published a counterexample to that assumption which changed the shape of the field.
The previous lesson set out compatibilism as a theory of what makes an action free. This lesson takes the more radical route: not arguing about how to interpret "could have done otherwise", but arguing that the phrase was never doing the work anyone thought it was doing.
The principle under attack
Frankfurt named the target the principle of alternate possibilities, and stated it as follows: a person is morally responsible for what he has done only if he could have done otherwise.
The principle is enormously plausible. It underwrites the excuses we all accept. The cashier who hands over money at gunpoint, the driver whose brakes fail, the man pushed into someone else: in each case what removes the blame seems to be that no other course was open. It is also the premise that makes the Consequence Argument matter. If determinism removes alternatives, and alternatives are necessary for responsibility, then determinism removes responsibility, and that two-step is why anyone outside a philosophy department cares about the first step.
Frankfurt's strategy is to construct a case where the alternatives are removed by something that plays no part in what actually happens.
Black and Jones
Jones is deciding whether to shoot a man. Unknown to him, a neurosurgeon called Black wants him to shoot, and has installed a device in Jones's brain. Black is an excellent judge of these things and can tell from some prior indicator, a twitch, a pattern of blood flow, whatever you like, which way Jones is about to decide. If the indicator shows that Jones is about to decide not to shoot, the device fires and produces the decision to shoot instead. If the indicator shows that Jones is about to decide to shoot, the device stays idle.
As it happens, Jones decides to shoot entirely on his own, for his own reasons, and Black never intervenes. He watches, ready, and does nothing.
Now the two verdicts. Jones could not have done otherwise: every path in which he begins to decide against shooting ends with the device producing the decision to shoot. And Jones is responsible: the actual sequence of events ran through his own deliberation, his own reasons and his own decision, exactly as it would have in a world containing no Black at all. Black's presence made no difference to anything that happened, and it is hard to see how a fact that made no difference to what happened can affect the responsibility for it.
If both verdicts stand, the principle of alternate possibilities is false. And if it is false, the Consequence Argument loses its bite: determinism may well remove the ability to do otherwise, and that removal turns out not to be what responsibility was ever tracking.
Frankfurt added a diagnostic point that is easy to miss and does most of the persuasive work. In the ordinary excusing cases, the inability to do otherwise is also the explanation of the act: the cashier hands over the money because of the gun. The excuse works through the explanation. In his case the inability is idle: Jones did not shoot because of Black, and would have shot in exactly the same way had Black never existed. So the principle, stated in its usual form, has been overgeneralising from cases where something else was doing the excusing.
Example. Distinguish these two cases and say why the first excuses and the second does not. First: a bank teller hands over the money because an armed robber threatens her. Second: a bank teller who has decided to embezzle hands over the money to an accomplice, unaware that an armed accomplice in the queue would have forced her to do it had she hesitated.
In the first, the threat explains the act. Remove the gun and she does not hand over the money, so the inability to do otherwise is part of the story of why she acted, and the excuse runs through that. In the second, the armed accomplice is causally idle: she hands over the money because she decided to steal, and the story of the act contains no mention of him. Take him out of the world and every step of what actually happened is unchanged. She had no alternative and she is fully to blame, which is exactly the pattern Frankfurt claims refutes the principle.
Now you. Someone objects that Jones is not responsible, because Black's device made the outcome inevitable and nobody is responsible for the inevitable. What has this objection missed?
Answer
It has confused the inevitability of the outcome with the source of the outcome. Frankfurt grants that the shooting was inevitable and denies that inevitability, by itself, has ever been what excuses. What excuses is that the agent was not the one who produced the act, and in this case he was: the causal path ran through his deliberation and not through the device. The objection also proves too much, since a man who wants to stay in a locked room, in Locke's case from the first lesson, faces an inevitable outcome and is plainly answerable for staying. Inevitability that operates through you is a different thing from inevitability that operates around you.
The dilemma defence
The counterexample did not go unanswered, and the best reply, developed by Robert Kane and stated sharply by David Widerker and Carl Ginet in the mid-1990s, attacks the prior indicator.
Black needs to know, before Jones decides, which way Jones is going to decide. So ask what the connection between the indicator and the decision is.
Take the first horn. Suppose the connection is deterministic, so that the twitch guarantees the decision. Then the case describes a world where Jones's decisions are determined by prior states, and an incompatibilist will say that Jones is not responsible in that world for exactly the reasons the Consequence Argument gives. The case would then be assuming the falsity of incompatibilism in order to refute a principle incompatibilists hold, which is question-begging.
Take the second horn. Suppose the connection is merely probabilistic, which is what an incompatibilist thinks the world is like at the moment of a free decision. Then the indicator does not guarantee anything. Jones might show the twitch associated with shooting and then decide not to shoot, so Black cannot rely on it, and to be sure of his outcome he would have to intervene before Jones decides, which turns the case into ordinary manipulation where nobody thinks Jones is responsible.
Either way, the case fails to do what it was built for. This is a good objection and it has been the centre of the literature for thirty years.
The main compatibilist counter is the flicker of freedom strategy, and the counter to the counter. Fischer's version concedes that Jones retains some alternative, perhaps the involuntary showing or not showing of the indicator, and argues that such alternatives are too thin to ground responsibility: they are not things Jones does, he has no control over them, and they are not the sort of thing that could make the difference between blame and exculpation. The demand is for a robust alternative, one the agent could have voluntarily taken and which would have been an exercise of control.
Example. Design a Frankfurt case and test it against the dilemma. A student is deciding whether to cheat in an exam. A device implanted by an examiner will force the decision to cheat if she shows signs of deciding otherwise. She cheats on her own. Where does the dilemma bite?
At the phrase "shows signs of deciding otherwise". If the signs are deterministically linked to what she will decide, then her decision was determined by prior states, and an incompatibilist denies responsibility for the same reason they deny it in any determined world, so the case cannot be used against them. If the signs are only probabilistically linked, the examiner cannot wait for them: she might display every sign of honesty and then cheat anyway, or the reverse, so no setting of the device both guarantees the outcome and stays out of the actual sequence. To make the case work, the device must be triggered by something that necessitates the decision without being part of it, and constructing such a trigger is the technical problem the next section is about.
Now you. Suppose the dilemma defence is right and no Frankfurt case can be built. Does the incompatibilist then win?
Answer
No, and this is the most important thing to take from the lesson. Failing to refute the principle of alternate possibilities leaves the principle standing, which is one premise of a two-premise argument; the other premise, that determinism removes alternatives, is what the Consequence Argument supplies, and a compatibilist may still deny that. More significantly, the leading incompatibilists themselves have largely stopped resting their case on alternatives. Pereboom, who defends the dilemma-proof buffer cases, is an incompatibilist arguing that Frankfurt was right about alternatives and that determinism defeats responsibility for a different reason entirely. The two sides have converged on the view that the interesting question is about the source of an action, not the number of futures available, and the lesson after this one is the argument that results.
Buffers and blockage
The technical problem the dilemma poses is precise: build a case in which the agent has no robust alternative, without using a deterministic link between a prior sign and the decision. Three strategies have been tried.
The first is blockage, proposed by David Hunt and developed by Eleonore Stump. Instead of an intervener who watches and reacts, imagine that all the neural pathways leading to any decision other than the actual one are simply blocked, from before the deliberation begins. Nothing is triggered by a prior sign, so no deterministic link is needed, and the agent's actual deliberation proceeds through unblocked channels exactly as it would have anyway. Critics reply that a mind with most of its pathways walled off is not obviously undergoing normal deliberation at all, and that the case may be a disguised form of determination rather than an alternative to it.
The second is simultaneous overdetermination, from Alfred Mele and David Robb in 1998. A deterministic process is set running in Jones's brain which will produce the decision to steal at a set time, while Jones's own indeterministic deliberation runs in parallel. If Jones decides to steal on his own first, his process wins and the implanted one is preempted; if he does not, the implanted process produces the decision. There is no prior sign anywhere, so the dilemma has nothing to grip. The dispute here is about what happens when two processes converge on the same result, which is an old and unresolved problem about causal preemption.
The third and most discussed is Derk Pereboom's buffer case. In his tax evasion example, a device is set so that Plum can decide to evade only if he first attains a specific level of attentiveness to his moral reasons, and the device prevents him from ever reaching that level, while otherwise leaving him entirely alone. Plum decides to evade on his own, without ever coming close to the buffer. The only alternative left to him is failing to reach a state he never reaches anyway, which is not something he does and not a course of action he could have taken.
It is the fairest summary of the area to say that none of the three has been generally accepted and none has been generally refuted. What all three share is the shape of the reply: keep the agent's actual deliberation untouched, and remove the alternatives by a mechanism that is not a reaction to a sign.
Example. Why does the buffer case avoid the dilemma that defeats the original Black and Jones story?
Because it removes the prior sign. Black needed to know in advance which way Jones would go, and the dilemma attacked the link that gave him that knowledge. Pereboom's device needs no forecast: it simply makes one route permanently unavailable, in advance and unconditionally, and then does nothing at all. Plum's deliberation may be as indeterministic as any libertarian wants, so no assumption of determinism is smuggled in, and yet the only thing he could have done other than decide to evade is fail to attain a level of attentiveness, which is not an action, not under his control, and not something a jury could regard as the difference between guilt and innocence. Whether an alternative that thin is genuinely irrelevant is the remaining live question.
Now you. Suppose a critic accepts the buffer case, agrees that alternatives are irrelevant, and remains an incompatibilist. What must their argument now look like?
Answer
It must run entirely through sourcehood. Having conceded that a determined agent's lack of alternatives is not what excuses, they need to show that determination spoils something else: that an agent whose deliberation is fixed by conditions in place before their birth is not the origin of what they do, in whatever sense origination is required for desert. That is precisely Pereboom's own position, which is why he builds the buffer cases himself rather than resisting them. It is also the reason this course spends two lessons on manipulation and constitutive luck and only one on the Consequence Argument: the modern dispute is about histories, not about branching futures.
What responsibility tracks instead
If alternatives are not what responsibility depends on, something else must be, and the answer the literature converged on is the actual sequence.
The idea is that responsibility supervenes on how the action was actually produced. Two agents whose deliberations run identically, step for step, must receive the same verdict, whatever differs in the surrounding possibilities. Black's presence in the room, the buffer that was never approached, the counterfactual robber in the queue: none of these belongs to the actual sequence, and none of them changes anything about how the decision was reached.
This is a genuinely powerful principle, and it explains why Frankfurt cases feel compelling rather than merely clever. It also explains what a theory of responsibility should be looking for: features of the actual causal path, such as whether the mechanism producing the decision responds to reasons, whether the agent's values were engaged, whether they knew what they were doing.
The principle cuts both ways, though, and the incompatibilist can use it too. An actual sequence has a history, and the history is part of how the action was actually produced. Whether "actual sequence" is read narrowly, covering the proximate mechanism, or widely, covering the whole causal ancestry back to the agent's formation, is exactly what separates a compatibilist from an incompatibilist about sourcehood. Frankfurt's counterexample settled that alternatives are irrelevant. It did not settle how far back the relevant sequence extends.
What the field looks like afterwards
Three things changed after 1969, and they explain the shape of the rest of this course.
First, responsibility and the ability to do otherwise came apart as topics. It is now standard to distinguish leeway views, which make responsibility depend on alternatives, from source views, which make it depend on where the action came from. Fischer's semi-compatibilism from the previous lesson is the clearest example: determinism removes leeway, responsibility survives, and no contradiction is involved because responsibility never needed leeway.
Second, the burden on incompatibilists shifted. An incompatibilist who wants to press the case has to show that determinism spoils sourcehood, not merely that it removes alternatives. That is a harder and more interesting claim, and the manipulation argument of the next lesson is the best attempt at it.
Third, and less often noticed, the ordinary intuition that Frankfurt cases exploit is not neutral between the two sides. What makes us judge Jones responsible is that the actual sequence ran through his own reasons and his own deliberation. That is a compatibilist-friendly criterion. An incompatibilist has to explain why an actual sequence that satisfies it is not enough, and the answer will be about the history of the agent's reasons rather than about the moment of decision. Once the argument is about histories, it is about upbringing, genes and manipulation rather than about physics, and the second half of this course lives there.