Libertarianism is a school of thought that says humans are free from physical determinism and all the other diverse forms of determinism.

Libertarians believe that strict determinism and freedom are incompatible. Freedom seems to require some form of indeterminism.

Most libertarians have been mind/body dualists who, following René Descartes, explained human freedom by a separate mind substance that somehow manages to act in the physical world. Some, especially Immanuel Kant, believed that our freedom only existed in a transcendental or noumenal world, leaving the physical world to be completely deterministic.

Religious libertarians say that God has given man a gift of freedom, but at the same time that God's foreknowledge knows everything that man will do.

In recent free will debates, these dualist explanations are called "agent-causal libertarianism." The idea is that humans have a kind of agency (an ability to act) that cannot be explained in terms of physical events.

One alternative is called "event-causal libertarianism," in which some events are uncaused or indeterministically caused. Note that eliminating strict determinism does not eliminate causality.

We can still have events that are caused by indeterministic prior events. And these indeterministic events have prior causes, but the prior causes are not sufficient to determine the events precisely. In modern physics, for example, events are only statistical or probabilistic. We can call this soft causality, meaning not pre-determined but still having a causal explanation.

Still another position is to say that human freedom is uncaused or simply non-causal. This would eliminate causality. Some philosophers think "reasons" or "intentions" are not causes and describe their explanations of libertarian freedom as "non-causal."

We can thus present a taxonomy of indeterminist positions.

It has often been claimed by some philosophers that libertarian accounts of free will are unintelligible. No coherent idea can be provided for indeterminism and chance, they say. They include the current chief spokesman for libertarianism, Robert Kane. ¹

The first libertarian, Epicurus, argued that as atoms moved through the void, there were occasions when they would "swerve" from their otherwise determined paths, thus initiating new causal chains.

The modern equivalent of the Epicurean swerve of atoms is quantum mechanical uncertainty, again a property of atoms. We now know that atoms do not just occasionally swerve, they move unpredictably whenever they are in close contact with other atoms.

Everything in the material universe is made of atoms in unstoppable perpetual motion. Deterministic paths are only the case for very large objects, where the statistical laws of atomic physics average to become nearly certain dynamical laws for billiard balls and planets.

Many determinists are now willing to admit that there is real indeterminism in the universe. ^2,3 Libertarians should agree with them that if indeterministic chance was the direct cause of our actions, that would not be freedom with responsibility.

Then determinists should agree that if chance was not a direct cause of our actions, it would do no harm. In which case, libertarians should be able to convince the determinists that if chance provides real alternatives to be considered by the adequately determined will, it provides real alternative possibilities for thought and action. It provides freedom and creativity.

Libertarians should give the determinists, at least the compatibilists, the kind of freedom they say they want, one that provides an adequately determined will for which we can take responsibility.