Alternative Possibilities are one of the key requirements for the freedom component of free will, critically needed for libertarian free will. They allow for what William James called open and ambiguous futures. The old page on Harry Frankfurt's denial of the Principle of Alternate Possibilities (PAP) can be found here. This Possibilities page is now about the philosophical difference between possibilities (especially those never realized) and the one realized actuality.
The existential and ontological status of mere "possibilities" has been debated by philosophers for many centuries. Diodorus Cronus dazzled his contemporaries in the fourth century BCE with sophisticated logical arguments, especially paradoxes, that "proved" there could be only one possible future. Diodorus' Master Argument is a set of propositions designed to show that the actual is the only possible and that some true statements about the future imply that the future is already determined. This follows logically from his observation that if something in the future is not going to happen, it must have been that statements in the past that it would not happen must have been true. Modern day "actualists" include Daniel Dennett, for whom determinism guarantees that the actual outcome is and always was the only possible outcome. The ancient philosophers debated the distinction between necessity and contingency (between the a priori and the a posteriori). Necessity includes events or concepts that are logically necessary and physically necessary, contingency those that are logically or physically possible. In the middle ages and the enlightenment, necessity was often contrasted with freedom. In modern times it is often contrasted with mere chance. Causality is often confused with necessity, as if a causal chain requires a deterministic necessity. But we can imagine chains where the linked causes are statistical, and modern quantum physics tells us that all events are only statistically caused, even if for large macroscopic objects the statistical likelihood approaches certainty for all practical purposes. The apparent deterministic nature of physical laws is only an "adequate" determinism. In modern philosophy, modal theorists like David Lewis discuss counterfactuals that might be true in other "possible worlds." Lewis' work at Princeton may have been inspired by the work of Princeton scientist Hugh Everett III. Everett's interpretation of quantum mechanics replaces the "collapse" of the wave function with a "splitting" of this world into multiple worlds.
The Quantum Mechanics of Alternative PossivilitiesAccording to the Schrödinger equation of motion, the time evolution of the wave function describes a "superposition" of possible quantum states. Standard quantum mechanics says that interaction of the quantum system with other objects causes the system to collapse into one of the possible states, with probability given by the square of the "probability amplitude." One very important kind of interaction is a measurement by an "observer." In standard quantum theory, when a measurement is made, the quantum system is "projected" or "collapsed" or "reduced" into a single one of the system's allowed states. If the system was "prepared" in one of these "eigenstates," then the measurement will find it in that state with probability one (that is, with certainty). However, if the system is prepared in an arbitrary state ψa, it can be represented as being in a linear combination of the system's basic eigenstates φn.
ψa = Σ cn | n >.where
cn = < ψa | φn >.The system ψa is said to be in "superposition" of those basic states φn. The probability Pn of its being found in a particular state φn is
Pn = < ψa | φn >2 = cn2 .
Harry Frankfurt's Denial of the Principle of Alternae Possibilites
Harry G. Frankfurt is the inventor of wildly unrealistic but provocative "thought experiments" designed to show that a person can be morally responsible for actions without the ability to "have done otherwise." Specifically, his goal is to provide a hypothetical example of an agent who is not free to choose among alternative possibilities, yet is still clearly responsible. Traditional arguments for free will require alternative possibilities so that an agent could have done otherwise, without which there is no moral responsibility. In the 1960's, the criticism that compatibilism could not provide the alternative possibilities needed to enable "doing otherwise" was disturbing some compatibilist thinkers. Frankfurt set out to defend compatibilism by providing hypothetical examples of agents who could not have done otherwise but are nevertheless clearly responsible. His work has undoubtedly contributed to the significant fraction of philosophers who call themselves compatibilist. Frankfurt's article encouraged many philosophers, notably John Martin Fischer, to ignore libertarian free will and emphasize moral responsibility. Fischer came to the extreme view that free will can be identified with moral responsibility. But they must be separated. Free will is a scientific question. Moral responsibility is a social and cultural question.
In 1969, Frankfurt famously defined what he called "The Principle of Alternate Possibilities" or PAP, then proceeded to deny it.
"a person is morally responsible for what he has done only if he could have done otherwise.”
Frankfurt's thought experiments are attacks on this principle. Considering the absurd nature of his attacks (Frankfurt asks us to imagine an agent who can control the minds of others, or a demon inside one's mind that can intervene in our decisions), the recent philosophical literature is surprisingly full of articles with "Frankfurt-type cases," logical counterexamples to Frankfurt's attempt to defend moral responsibility in the absence of alternative possibilities. Frankfurt changed the debate on free will and moral responsibility with his hypothetical intervening demon. For example, John Martin Fischer's semicompatibilism assumes with Frankfurt that we can have moral responsibility, even if determinism (and/or indeterminism) are incompatible with free will. Frankfurt's basic claim is as follows:
"The principle of alternate possibilities is false. A person may well be morally responsible for what he has done even though he could not have done otherwise. The principle's plausibility is an illusion, which can be made to vanish by bringing the relevant moral phenomena into sharper focus."Frankfurt posits a counterfactual demon who can intervene in an agent's decisions if the agent is about to do something different from what the demon wants the agent to do. Frankfurt's demon will block any alternative possibilities, but leave the agent to "freely choose" to do the one possibility desired by the demon. Frankfurt claims the existence of the hypothetical control mechanisms blocking alternative possibilities are irrelevant to the agent's free choice. This is true when the agent's choice agrees with the demon, but obviously false should the agent disagree. In that case, the demon would have to block the agent's will and the agent would surely notice.
(IRR) There may be circumstances that in no way bring it about that a person performs a certain action; nevertheless, those very circumstances make it impossible for him to avoid performing that action.
Compatibilists have long been bothered by alternative possibilities, apparently needed in order that agents "could do otherwise." They knew that determinism allows only a single future, one actual causal chain of events. They were therefore delighted to get behind Frankfurt's examples as proofs that alternative possibilities, perhaps generated in part by random events, did not exist. Frankfurt argued for moral responsibility without libertarian free will.
Note, however, that Frankfurt assumes that genuine alternative possibilities do exist. If not, there is nothing for his counterfactual intervening demon to block. Furthermore, without alternatives, Frankfurt would have to admit that there is only one "actual sequence" of events leading to one possible future. "Alternative sequences" would be ruled out. Since Frankfurt's demon, much like Laplace's demon, has no way of knowing the actual information about future events - such as agent's decisions - until that information comes into existence, such demons are not possible and Frankfurt-style thought experiments, entertaining as they are, can not establish the compatibilist version of free will.
Incompatibilist libertarians like Robert Kane, David Widerker, and Carl Ginet have mounted attacks on Frankfurt-type examples, in defense of free will. Their basic idea is that in an indeterministic world Frankfurt's demon cannot know in advance what an agent will do. As Widerker put it, there is no "prior sign" of the agent's de-liberate choice. In information theoretic terms, the information about the choice does not yet exist in the universe. So in order to block an agent's decision, the demon would have to act in advance, and that would destroy the presumed "responsibility" of the agent for the choice, whether or not there are available alternative possibilities. We could call this the "Information Objection." And note that no matter how many alternative possibilities are blocked by Frankfurt's hypothetical intervener, the simple alternative of not acting always remains open, and in cases of moral actions, not acting almost always has comparable moral significance. This could be called the "Yes/No Objection." Here is a discussion of the problem, from Kane's A Contemporary Introduction to Free Will, 2005, (p.87)
5. The Indeterminist World Objection While the "flicker of freedom" strategy will not suffice to refute Frankfurt, it does lead to a third objection that is more powerful. This third objection is one that has been developed by several philosophers, including myself, David Widerker, Carl Ginet, and Keith Wyma.5 We might call it the Indeterministic World Objection. I discuss this objection in my book Free Will and Values. Following is a summary of this discussion:Suppose Jones's choice is undetermined up to the moment when it occurs, as many incompatibilists and libertarians require of a free choice. Then a Frankfurt controller, such as Black, would face a problem in attempting to control Jones's choice. For if it is undetermined up to the moment when he chooses whether Jones will choose A or B, then the controller Black cannot know before Jones actually chooses what Jones is going to do. Black may wait until Jones actually chooses in order to see what Jones is going to do. But then it will be too late for Black to intervene. Jones will be responsible for the choice in that case, since Black stayed out of it. But Jones will also have had alternative possibilities, since Jones's choice of A or B was undetermined and therefore it could have gone either way. Suppose, by contrast, Black wants to ensure that Jones will make the choice Black wants (choice A). Then Black cannot stay out of it until Jones chooses. He must instead act in advance to bring it about that Jones chooses A. In that case, Jones will indeed have no alternative possibilities, but neither will Jones be responsible for the outcome. Black will be responsible since Black will have intervened in order to bring it about that Jones would choose as Black wanted.In other words, if free choices are undetermined, as incompatibilists require, a Frankfurt controller like Black cannot control them without actually intervening and making the agent choose as the controller wants. If the controller stays out of it, the agent will be responsible but will also have had alternative possibilities because the choice was undetermined. If the controller does intervene, by contrast, the agent will not have alternative possibilities but will also not be responsible (the controller will be). So responsibility and alternative possibilities go together after all, and PAP would remain true — moral responsibility requires alternative possibilities — when free choices are not determined.6 If this objection is correct, it would show that Frankfurt-type examples will not work in an indeterministic world in which some choices or actions are undetermined. In such a world, as David Widerker has put it, there will not always be a reliable prior sign telling the controller in advance what agents are going to do.7 Only in a world in which all of our free actions are determined can the controller always be certain in advance how the agent is going to act. This means that, if you are a compatibilist, who believes free will could exist in a determined world, you might be convinced by Frankfurt-type examples that moral responsibility does not require alternative possibilities. But if you are an incompatibilist or libertarian, who believes that some of our morally responsible acts must be undetermined you need not be convinced by Frankfurt-type examples that moral responsibility does not require alternative possibilities.
There are also many defenders of Frankfurt's attack on alternative possibilities, notably John Martin Fischer. Many of these positions appear in the 2006 book Moral Responsibility and Alternative Possibilities, edited by David Widerker and Michael McKenna.Normal | Teacher | Scholar