Objections and Responses to the Existence of Free Choice

Samuel Johnson once observed: "All theory is against the freedom of the will; all experience for it."¹ He was only half right. As we will see, St. Thomas Aquinas offers a strong theory in favor of the freedom of choice. In this essay, I will weigh three objections to fully voluntary acts: those derived from neuroscience, physicalist determinism, and the problem of habituation. Although many other objections to free choice exist, these represent some of the most serious assaults on the idea of human freedom, and therefore human responsibility. In a final section, I will address Aquinas's claim that freedom is rooted in reason. With these considerations in place, we will be well on our way to establishing a solid theory of morality in all its subtlety and richness.

First Objection: The Experiments of Benjamin Libet

Scientists and thinkers who argue against the existence of free choice very frequently cite the work of neurobiologist Benjamin Libet.² For many, Libet's experiments demonstrate that human action is not caused by an individual's will or intention to act, and therefore that voluntary action is an illusion. Let us see why they think so.

Libet's goal in his experiments was to determine how or whether a voluntary act arises in relation to brain functioning.³ In order to do this, he and his colleagues devised a way to ask test subjects about what he defined as a "voluntary action." For Libet, a voluntary action has three aspects: (1) it arises from within a person and is not determined by an external stimulus; (2) it is free from "externally imposed restrictions or compulsions that directly or immediately control subjects' initiation and performance of the act"; and (3) "most important, subjects feel introspectively that they are performing the act on their own initiative and that they are free to start or not to start the act as they wish."⁴ Accordingly, Libet asked the subjects "to perform a simple quick flexion of the wrist or fingers at any time they felt the 'urge' or desire to do so," ensuring that the movement was spontaneous and wholly unforced.⁵ They were then to look at a spot of light that revolved around a clock face in a little over two and a half seconds. They were to report for each wrist or finger movement precisely where the spot was on the clock when they were first aware of wanting to flex.

The results of the experiment were striking. Measuring brain electrical activity, Libet found that a "readiness potential" (RP) to act arose almost 300 milliseconds before the subject was aware of wanting to act. That is, the brain was already active before the individual became conscious of a movement in his desire to flex. This is represented in the figure below.⁶

It should be emphasized that, although the brain was active prior to their conscious awareness of a desire to act, the subjects all reported that their movements were self-initiated, that they believed they were in control of whether or not to act, and that they were aware of no external or psychological pressures that affected the time when they decided to act.⁷ The importance of these results is indicated by the fact that they have generated a cottage industry of responses and analyses.

Many interpreters were astonished by Libet's findings.⁸ Supposing that the subject's will is the cause of his movement, it seems to follow that the will would be the cause of the brain's activity that initiates the movement. Thus, one's brain activity should come after or at least be simultaneous with one's decision to move, but certainly not before it. Because the brain activity preceded the subject's desire to act, there seems to be no reason to hold that the subject's will initiated the series of movements that led to his flexion. Instead, as Harvard psychologist Daniel Wegner put it, Libet's experiments suggest that, "voluntary action is a...