Most people feel like they have control over what they do and that therefore they and all other people who are mentally competent are ultimately responsible for their actions. The different ways of interpreting this phenomenon can be considered different understandings of the term “free will”. This term has different meanings in different contexts and the meaning that one gives to this term has important implications for materialism and dualism.
Determinism, the belief that all events are caused by prior events and that all eventual outcomes are predetermined, is often understood to be incompatible with free will, though not to so called compatiblists such as Daniel Dennett, who strongly believes in determinism but says he also believes in what he calls a variety of free will 1. The variety he speaks of is not libertarian free will, which traditionally is understood to mean that there is no causal chain that determines an agent’s actions prior to the agent freely choosing them.
When Dennett speaks of free will, he is instead referring to the abilities of certain complex beings living within a deterministic system. Beings have Dennett’s variety of free will if they are able to conceptualize external reality and to mentally represent and deliberate over possible actions, even though this system is deterministic and therefore the eventual actions performed by each being are predetermined.
For some people though, it is not enough that they simply deliberate over multiple possible options if the end result is ultimately predetermined by physical laws. Some philosophers, such as Robert Kane, have argued that people have libertarian free will. Kane does not deny that the laws of physics govern the operations of the human body, but he believes it is possible to reconcile the physical world with libertarianism 2.
There are problems with accepting libertarianism including the apparent scientific counterevidence and the difficulty in coming up with a coherent metaphysical system to support it. For starters, the physical world appears to be deterministic. Overwhelming empirical evidence shows that everything that happens is caused by physical laws, not by the chosen actions of agents. The human body, including the brain, is physical and is driven by physical laws.
1 Dennett, Daniel. Freedom Evolves. Cambridge, MA, USA: MIT Press, 2003.
2 Kane, Robert. The Significance of Free Will. Oxford: Oxford University Press, 1996.