Determinism is a scientific perspective that specifies that events occur in completely predictable ways as a result of natural and physical laws.

Determinism, which has also sometimes been called necessitarianism, is a philosophical concept that states every event, including those involving human decisions and actions (such as moral choices), are ultimately determined by circumstances external to those events (in other words, by the natural and physical laws that govern the universe).

Some philosophers extolling the principles of determinism contend that humans do not have free will; thus, every action is predestined and freedom of choice is an illusion. As a consequence, these philosophers contend that people should not be held responsible for their actions. The philosophy based on this strict interpretation of determinism, that humans have no control on their future, is called fatalism. By contrast to fatalism, determinism asserts that humans have some influence on their future and that this influence is based on past and present events.

Foundations of determinism

Since ancient times, the origins of human behavior have been attributed to hidden or mystical forces. The Greek philosopher Democritus (460 B.C.–370 B.C.) speculated, for example, that objects in the world consist of atoms; included among these objects is the soul, which is made of finer, smoother, and more spherical atoms than other physical objects. He rejected the concept of free will and claimed that all human behavior results from prior events. Some philosophers have advanced the argument that human behavior is deterministic, although many have resisted the idea that human beings merely react to external events and do not voluntarily select behaviors.

French scholar Pierre-Simon, Marquis de Laplace (1749–1827) developed the philosophical foundations that would eventually become determinism. He surmised that if an individual knows all the forces exerted by nature at any given moment, then that person can ascertain the past and the future.

There is a dilemma in explaining human behavior through psychological principles. On the one hand, if psychology is a science of behavior, then there should be laws that can predict or explain behavior, just as there are gravitational laws to predict the behavior of a falling object with mass. On the other hand, if humans control their own behaviors and possess free will, then behavior is unpredictable and is determined by individual choice. The controversy entails how the human mind and body are defined and whether they are separate entities. Whether the mind is not subject to the same laws as the body becomes a question.

The dilemma posed by determinism and free choice

German physician and philosopher Wilhelm Wundt (1832–1920) attempted to distinguish between determinism and indeterminism (the concept that not all events are entirely determined by pre-existing causes) by suggesting that psychological processes can be creative and free whereas the physiological processes in the brain are determined by physical causation. This distinction does not resolve the delimma for psychology, however, because psychologists want to study mental processes within a scientific framework, thus subject to scientific laws.

Other psychologists, such as William James (1842–1910), who was interested in religion and believed in free will, recognized this delimma but were reluctant to abandon the concept that behaviors are not freely enacted. At one point, James suggested that mind and body operate in tandem; however, on another occasion he concluded that they interacted. James struggled with the dilemma and, like others, was unable to resolve it.

Skinner, Freud support determinism differently

The psychologist with the greatest influence in this area was American psychologist and social philosopher B. F. Skinner (1904–1990). He adopted a stance called radical behaviorism, which disregarded free will and the internal causes of behavior. All behavior, Skinner maintained, was determined through reinforcement contingencies, that is, the pattern of reinforcements and punishments in an individual's life. Although critics have claimed that Skinner's concept of determinism denied people of their humanity, he maintained that his approach could actually lead to more humane societies. For example, if people were not responsible for negative behaviors, they should not be punished, for they had no control over their behaviors. Instead, the environment that reinforced the unwanted behaviors should be changed so that desirable behaviors receive reinforcement and increase in frequency.

Austrian neurologist Sigmund Freud (1856–1939) defined determinism in terms of the unconscious and contended that behavior is caused by internal, mental mechanisms. In some ways, Freud was more extreme than was Skinner, who acknowledged that some behaviors are not predictable. The main difference between Freud and Skinner involved the origin of causation; Freud believed in underlying physiological processes while Skinner opted to focus on external causes. Thus, even though Freudians and Skinnerians differ on almost every conceivable dimension, they have at least one commonality in their reliance on determinism.

Theories of statistical determinism and chaos

Those scientists who believe that behaviors are determined have recognized the difficulty in making explicit predictions. They have developed the concept of statistical determinism, which had its origin in the works of Belgian mathematician and astronomer Lambert Adolphe Quetelet (1796–1874). Quetelet is credited with introducing statistics to the social sciences. The theory of statistical determinism states that, even though behaviors are determined by fixed laws, predictions will never be exact because so many different and complex factors, most of them unknown, affect actions, which result in generally accurate predictions.


A psychological theory of human development that states humans can be conditioned to respond in specific ways to specific stimuli and that given the correct stimuli, behaviors of individuals can be controlled.
Natural law—
Also called the law of nature, a group of universal principles considered to be inherent within the natural and physical world and which influence human actions.

Chaos theory, which developed in the second half of the twentieth century, attempts to explain the nature of and predictions about complex events such as behaviors. This theory suggests that in a causeeffect situation, small differences in initial conditions may lead to very different outcomes. American mathematician Edward Norton Lorenz (1917–2008) pioneered the development of chaos theory in the early 1960s. His work in chaos theory culminated with the publication of the 1963 paper “Deterministic Nonperiodic Flow” in the Journal of the Atmospheric Sciences. This theory supports the notion that behaviors may not be completely predictable even though they may be dictated by fixed natural laws.

See also Behaviorism ; Conditioning .



Atmanspacher, Harald, and Robert Bishop, eds. Between Chance and Choice: Interdisciplinary Perspectives on Determinism. Charlottesville, VA: Imprint Academic, 2002.

Campbell, Joseph Keim, Michael O'Rourke, and David Shier, eds. Freedom and Determinism. Cambridge: MIT Press, 2004.

Franklin, Richard Langdon. Freewill and Determinism: A Study of Rival Conceptions of Man. London: Routledge and K. Paul, 1968.


Lorenz, Edward N. “Deterministic Nonperiodic Flow.” Journal of the Atmospheric Sciences 20, 2 (1963): 130–41.


Overbye, Dennis. “Free Will: Now You Have It, Now You Don't.” New York Times. (accessed July 24, 2015).

The Great Debate. “Determinism and Free Will in Science and Philosophy.” (accessed July 24, 2015).


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