Recently, the question of whether our notions of free will, along with whether our responsibility-holding practices that appear to be based on free will, can survive in light of discoveries from the behavioral and brain sciences was named as one of the Top Ten Philosophical Issues of the 21st Century. The interest in free will and how discoveries in neuroscience and psychology affect our beliefs and attitudes about free will extends well beyond the halls of philosophy departments. The topic has also attracted a lot of interest from neuroscientists, biologists, and psychologists . And, of course, these very debates are of central interest to neuroethicists. The wide range of interests in these debates is a symptom of the fact that these debates matter: The debate over what people believe about free will and how discoveries in the behavioral and brain sciences might impact these beliefs matter for a wide range of theoretical, and perhaps more importantly, practical reasons. Much of the empirical research in this area also points to the need for a valid and reliable tool for measuring people’s beliefs about free will. Below, I touch on some of the reasons why people’s belief in free will matters, and I introduce a new tool for measuring beliefs about free will, the Free Will Inventory, which was published in this month’s issue of Consciousness and Cognition .
Whether people believe in free will matters. People’s beliefs in free will impact their behaviors. For example, experimental studies have shown that telling people they don’t have free will increases cheating and stealing, decreases prosocial behaviors and increases aggression, increases conformity, reduces self-control, and impairs the detection of errors. Other studies have shown that belief in free will is positively correlated with job performance of day laborers, and belief in free will is positively related to expectations of future occupational success in college students. These findings suggest that believing in free will may be instrumentally valuable from the standpoints of positive psychology and public morality.
These recent findings also highlight the importance of having valid and reliable tools for measuring beliefs in free will and related constructs. While the gathering data suggests that diminishing people’s belief in free will leads to all kinds of changes in behavior, the validity of these findings depends in part on the validity and reliability of the scales used to measure people’s beliefs about free will and related constructs. For example, the paradigms used in most of the above-mentioned experimental research involve one group of participants reading an anti-free will passage or reading a series of anti-free will statements. However, the anti-free will primes used in these experiments make claims that go beyond simple claims regarding the existence of free will. For example, some of the anti-free will statements also make claims that support belief in determinism (the view that the state of a system, plus the laws that govern that system, specify all subsequent states of the system) and challenge beliefs in dualism (the view that the mind and body are separate entities). It remains an open question whether these changes in behavior are best explained by changes in beliefs in free will, by changes in beliefs in determinism, by changes in believes in dualism, or some combination of changes in beliefs.
The ability to tease apart these explanations depends, in large part, on having psychometric tools that have the precision and specificity necessary to accurately measure beliefs in free will and related constructs such as determinism and dualism. While psychometric tools for measuring beliefs in free will and determinism exist, these tools are not without their problems. For example, many of the existing tools simply assume that free will and determinism are incompatible with each other, and, worse yet, often define free will and determinism as polar opposites of each other. Such an assumption rules out by fiat the ability of people to express a pattern of beliefs that is compatible with the philosophically rich tradition known as compatibilism, or the view that free will and determinism are compatible. As it turns out, this is an important mistake. There is accumulating evidence that compatibilist intuitions are more widespread than philosophers and psychologists have traditionally assumed . In other words, many of the previous psychometric tools for measuring beliefs about free will not only rule out the ability for people to express agreement with a theoretically rich philosophical position but also rule out the ability to express patterns of beliefs that may actually be common among non-philosophers (i.e. most of society)! Though some more recent psychometric tools for measuring beliefs in free will avoid this mistake, these more recent tools still fail to measure these constructs in a way that is useful for all stakeholders in these debates. For example, the ways these constructs are defined and measured often appear theoretically uninteresting (if not theoretically confused) from the philosopher’s point of view. Furthermore, these tools often have just-barely acceptable psychometric properties from the psychologist’s point of view, which again points to the possibility of problems of definition and measurement. Furthermore, none of the existing measures measure people’s beliefs in dualism, which is itself an important construct that is often claimed to be relevant for how people think about free will [e.g., 5].
What people believe about free will matters. Whether discoveries in science challenge the existence of free will depends a great deal on what we believe about free will. For example, if we believe that free will requires human behavior to be unpredictable in principle, and if discoveries in science provide evidence that all behavior is in principle fully predictable, then these discoveries would challenge the existence of free will … or would at least challenge the existence of the sort of free will that we believe in. However, if we didn’t believe that free will requires unpredictability in principle, then these sorts of discoveries would be irrelevant to the free will debate … or would at least be irrelevant to our beliefs about free will. In other words, determining what sorts of discoveries are relevant to free will depends a lot on what people believe about free will.
Unfortunately, the existing psychometric tools for free will beliefs primarily measure the extent to which people believe in free will. These tools provide very little insight into what people believe about free will. In other words, these tools can tell you whether someone believes in free will a little, a lot, or not at all; but these tools cannot tell you whether free will requires unpredictability or dualism or the ability to act outside the laws of nature. And this is an important oversight. We need tools that not only measure how much people believe in free will, but we also need tools that measure what people believe about free will.
Given the importance of having a good measurement tool that is useful to a wide range of stakeholders in the debate, a diverse research team that was comprised of philosophers and psychologists, compatibilists and incompatibilists recently set out to develop a new psychometric tool for measuring beliefs in free will and related constructs. This team was led by the philosopher Thomas Nadelhoffer and included myself, Eddy Nahmias, Chandra Sripada, and Lisa Ross. The new tool, The Free Will Inventory (FWI), was published in this month’s issue of Consciousness and Cognition. The FWI consists of two parts. The first part consists of three subscales: one that measures belief in free will, one that measures belief in determinism, and one that measures beliefs in dualism. While part 1 of the FWI measures people’s beliefs in free will, determinism, and dualism, part 2 measures people’s beliefs about free will and these related concepts (e.g., does free will depend on being unpredictable, on having an immaterial soul, on being able to act at least partially independent of the laws of nature).
While no psychometric tool is perfect, we hope we have developed a tool that avoids some of the problems that plagued the earlier tools and that is of interest to a wider range of stakeholders in the debate, from the psychologist to the philosopher, from the neuroscientist to the neuroethicist, and to anyone else who is interested in rigorously exploring people’s beliefs in and about free will.
 For recent, accessible multi-disciplinary discussion of how the brain and behavior sciences might inform the free will debate, see the Chronicle of Higher Education special series on "Is Free Will an illusion". For a thorough introduction to some of the best thinking on the topic, see: Sinnott-Armstrong, W. (2014). Moral Psychology, Vol. 4: Free Will and Moral Responsibility. Cambridge, MA: MIT Press.
 Nadelhoffer, T., Shepard, J., Nahmias, E., Sripada, C., & Ross, L.T. (2014). The free will inventory: Measuring beliefs about agency and responsibility. Consciousness and Cognition, 25, 27-41.
 For recent reviews, see: Baumeister, R.F., & Brewer, L.E. (2012). Believing versus disbelieving in free will: Correlated and consequences. Social and Personality Psychology Compass, 6, 736-745. and Rigoni, D. & Brass, M. (2014). From intentions to neurons: Social and neural consequences of disbelieving in free will. Topoi, 33, 5-12.
 A review of much of this research is discussed in the introduction of the paper on the FWI. See: Nadelhoffer, T., Shepard, J., Nahmias, E., Sripada, C., & Ross, L.T. (2014). The free will inventory: Measuring beliefs about agency and responsibility. Consciousness and Cognition, 25, 27-41.
 Montague, P.R. (2008). Free will. Current Biology, 18, 584-585.
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Shepard, J. (2014). Why people's beliefs in free will matter: Introducing the Free Will Inventory. The Neuroethics Blog. Retrieved on , from http://www.theneuroethicsblog.com/2014/04/why-peoples-beliefs-about-free-will.html