1. The Garden of Forking Paths
“There is a disputation that will continue till mankind is raised from the dead, between the necessitarians and the partisans of free will.”
These are the words of Jalalu’ddin Rumi, 13th century Persian poet and Sufi Muslim philosopher. The problem of free will of which Rumi speaks has arisen in human history whenever humans have reached a higher stage of self-consciousness about how profoundly the world may influence their behavior in ways unknown to them and beyond their control. The advent of doctrines of determinism or necessity in the history of ideas is an indication that this higher stage of awareness has been reached.
Determinist or necessitarian doctrines have taken many historical forms. People have wondered at various times whether their actions might be determined by Fate or God, by the laws of physics or of logic, by heredity or environment, psychological or social conditioning, and so on. But there is a core idea running through all these historical doctrines of determinism which shows why they may seem to threaten free will. They all imply that, given the past at any time and the laws governing the universe, there is only one possible future. Whatever happens is therefore inevitable or necessary (it cannot but occur), given the past and the laws.
Consider, by contrast, what free will requires. We believe we have free will when we view ourselves as beings capable of influencing the world in various ways. Open alternatives seem to lie before is. We reason and deliberate among them and choose. We feel (1) it is “up to us” what we choose and how we act; and this means we could have chosen or acted otherwise. As Aristotle said, “when acting is ‘up to us,’ so is not acting.” This “up-to-us-ness” also suggests that (2) the ultimate sources of our actions lie in us and not outside us in factors beyond our control.
To illustrate, suppose a young woman has just graduated from law school and she has a choice between joining a law firm in Chicago or a different firm in New York. If she believes her choice is a free choice (made “of her own free will,” as we say), she must believe both options are “open” to her while she is deliberating. She could choose either one. (If she did not believe this, what would be the point of deliberating?) But that means she believes there is more than one possible path into the future available to her and it is “up to her” which of these paths will be taken.
Such a picture of an “open future” with forking paths—a “garden of forking paths,” it has been called by the celebrated novelist Jorge Luis Borges —is essential to our understanding of free will. And this picture seems to many persons to conflict with determinism, which implies that there is only one possible future at any time, given the past and laws of nature.
(Illustration: Garden of Forking Paths)
Those who are convinced, for these and other reasons, that there is a conflict between free will and determinism, are called incompatibilists about free will in modern free will debates. They believe free will and determinism are incompatible—so that a world in which all events were determined or necessitated would not be hospitable to free will. If these incompatibilists also believe that a free will in this incompatibilist sense exists, so that determinism is false, they are called libertarians about free will.
I am both an incompatibilist and a libertarian about free will. Most libertarians about free will typically believe that a free will that is incompatible with determinism is required for us to be truly morally responsible for our actions. Genuine free will, we believe, could not exist in a world completely determined by Fate or God, the laws of physics or logic, heredity and environment, or other factors beyond our control. In writings over the past forty years, I’ve argued that such a libertarian view represents the traditional idea of free will that has been in dispute for centuries when philosophers have discussed “the problem of free will.”
2. Modern Challenges
Yet this traditional nondeterminist or libertarian conception of free will has been under attack by many modern thinkers, philosophers and scientists alike, who have come to believe that such an idea of free will is outmoded and incoherent and that it has no place in the modern scientific picture of the world. It is worth asking whether and how these modern attacks might be answered. For much is at stake, it seems to me, in knowing whether we do or do not have a freedom of the will of the ultimate kind that libertarians defend.
The modern attack on this traditional idea of free will has two parts.
1. The first part comes from compatibilists about free will, who argue that, despite any appearances to the contrary, determinism does not really conflict with free will.
Compatibilists typically argue that all the freedoms we care about in everyday life—e.g., freedoms from coercion or compulsion, from physical restraint or political oppression—are compatible with determinism. Even if the world should turn out to be deterministic, they argue, we could still distinguish between being free from constraints on our freedom (such as coercion, compulsion or oppression) and not being free from these constraints; and we would prefer to be free from such constraints on our freedom rather than not, even in a determined world.
So, questions about whether determinism is true or not, according to compatibilists, are irrelevant to whether or not we have the freedoms we really care about. All the varieties of free will “worth wanting” (as a modern compatibilist, Daniel Dennett, has put it) do not require the falsity of determinism for us to possess them, as the traditional libertarian view of free will suggests.
This compatibilist view of free will and determinism has a long history. It was held by the Stoic philosophers, among others, in ancient times. But it has become especially popular in modern times. Influential philosophers of the modern era, such as Thomas Hobbes, John Locke, David Hume and John Stuart Mill were all compatibilists. They saw compatibilism as a way of reconciling ordinary experience of being free with modern scientific views about the universe and human beings.
And compatibilism continues to be popular among philosophers and scientists today for similar reasons. If compatibilists are right, we can have both free will and determinism. And we need not worry that increasing scientific knowledge about nature and human beings will somehow undermine our ordinary convictions that we are free and responsible agents.
2. The second part of the modern attack on a traditional free will that is incompatible with determinism goes further. The claim here is that an incompatibilist free will is impossible or unintelligible and has no place in the modern scientific picture of the world. It is not a kind of freedom we could have anyway.
This familiar criticism is related to an ancient dilemma: If free will is not compatible with determinism, it doesn’t seem to be compatible with indeterminism either (the opposite of determinism). Events that are undetermined, such as quantum jumps in atoms, happen merely by chance. If free actions were undetermined, as libertarians claim, it seems that they too would happen by chance. But chance events are not under the control of anything, hence not under the control of agents. Suppose a choice resulted from undetermined quantum events in a person’s brain. Would this amount to a free and responsible choice? It seems that undetermined events in the brain or body would be more likely to undermine our freedom rather than to enhance it.
This problem has also been noted since ancient times. The ancient Epicurean philosophers argued that the atoms must sometimes “swerve” in undetermined or chance ways from their appointed paths if there was to be room in nature for freedom of will or choice. But the many critics of the Epicureans, such as the Stoics, cried out in opposition: How could the chance swerves of the atoms help with free will? Free will is not mere chance.
In response to such criticisms through the centuries, defenders of a nondetermined free will have often appealed to obscure and mysterious forms of agency or causation to defend their view. Indeterminism or chance in the natural order is necessary for free will, they say, but it is not enough. Some other “extra factors” must fill the “causal gaps” in nature left by chance. Thus, in order to explain how free actions can escape the clutches of physical causes and laws without merely occurring by chance, defenders of libertarian free will have posited transempirical power centers, immaterial minds, noumenal selves outside space and time, unmoved movers, uncaused causes and other unusual forms of agency or causation.
This is a natural way to think, but it has invited down through the centuries charges of obscurity or mystery against incompatibilist and libertarian views of free will. Even some of the greatest modern defenders of these views, such as Immanuel Kant, have argued that we need to believe in a free will that is incompatible with determinism to make sense of morality and genuine responsibility. But we can never completely understand such a freedom in scientific terms.
This two-part modern attack leads to two questions that have been central to modern debates about free will that are addressed in the next two sections. The first is The Compatibilist Question: Is free will compatible or incompatible with determinism? The second is The Intelligibility Question: Can one make sense of an incompatibilist or nondeterminist free will without reducing it to mere chance or to mystery, and can such a view be reconciled with modern scientific views of humans and the cosmos?
I believe that if we are to make progress in dealing with age-old disputes about free will, we must rethink the answers to both these questions from the ground up; and that is done in the next few parts.
 Libertarianism about free will should not be confused with the doctrine of political libertarianism, which advocates minimal government. Both doctrines have an interest in freedom (from the Latin liber meaning “free”). But being a libertarian about free will—believing in a free will that is incompatible with determinism—does not necessarily commit one to any particular political doctrine. Libertarians about free will may and do hold differing views in political philosophy.