Determinism is the philosophical proposition that every event, including human cognition and behaviour, decision and action, is causally determined by an unbroken chain of prior occurrences. With numerous historical debates, many varieties and philosophical positions on the subject of determinism exist from traditions throughout the world.
It is a popular misconception that determinism necessarily entails that humanity or individual humans have no influence on the future and its events (a position known as fatalism); however, determinists believe that the level to which human beings have influence over their future is itself dependent on present and past. Causal determinism is associated with, and relies upon, the ideas of materialism and causality. Some of the main philosophers who have dealt with this issue are Steven M. Cahn, Omar Khayyám, Thomas Hobbes, Baruch Spinoza, Gottfried Leibniz, David Hume, Baron d'Holbach (Paul Heinrich Dietrich), Pierre-Simon Laplace, Arthur Schopenhauer, William James, Friedrich Nietzsche and, more recently, John Searle, Ted Honderich, and Daniel Dennett.
Mecca Chiesa notes that the probabilistic or selectionistic determinism of B.F. Skinner comprised a wholly separate conception of determinism that was not mechanistic at all. A mechanistic determinism would assume that every event has an unbroken chain of prior occurrences, but a selectionistic or probabilistic model does not.
The exact meaning of the term determinism has historically been subject to several interpretations. Some, called Incompatibilists, view determinism and free will as mutually exclusive. The belief that free will is an illusion is known as Hard Determinism. Others, labeled Compatibilists, (or Soft Determinists) believe that the two ideas can be coherently reconciled. Incompatibilists who accept free will but reject determinism are called Libertarians — not to be confused with the political sense. Most of this disagreement is due to the fact that the definition of free will, like that of determinism, varies. Some feel it refers to the metaphysical truth of independent agency, whereas others simply define it as the feeling of agency that humans experience when they act.
Ted Honderich, in his book How Free Are You? - The Determinism Problem gives the following summary of the theory of determinism:
In its central part, determinism is the theory that our choices and decisions and what gives rise to them are effects. What the theory comes to therefore depends on what effects are taken to be... [I]t is effects that seem fundamental to the subject of determinism and how it affects our lives.
Causal (or nomological) determinism is the thesis that future events are necessitated by past and present events combined with the laws of nature. Such determinism is sometimes illustrated by the thought experiment of Laplace's demon. Imagine an entity that knows all facts about the past and the present, and knows all natural laws that govern the universe. Such an entity might, under certain circumstances, be able to use this knowledge to foresee the future, down to the smallest detail. Simon-Pierre Laplace's determinist dogma (as described by Stephen Hawking) is generally referred to as "scientific determinism" and predicated on the supposition that all events have a cause and effect and the precise combination of events at a particular time engender a particular outcome. This causal determinism has a direct relationship with predictability. (Perfect) predictability implies strict determinism, but lack of predictability does not necessarily imply lack of determinism. Limitations on predictability could alternatively be caused by factors such as a lack of information or excessive complexity. An example of this could be found by looking at a bomb dropping from the air. Through mathematics, we can predict the time the bomb will take to reach the ground, and we also know what will happen once the bomb explodes. Any small errors in prediction might arise from our not measuring some factors, such as puffs of wind or variations in air temperature along the bomb's path.
Logical determinism is the notion that all propositions, whether about the past, present or future, are either true or false. The problem of free will, in this context, is the problem of how choices can be free, given that what one does in the future is already determined as true or false in the present. This is refered to as the problem of future contingents.
Additionally, there is environmental determinism, also known as climatic or geographical determinism which holds the view that the physical environment, rather than social conditions, determines culture. Those who believe this view say that humans are strictly defined by stimulus-response (environment-behavior) and cannot deviate. Key proponents of this notion have included Ellen Churchill Semple, Ellsworth Huntington, Thomas Griffith Taylor and possibly Jared Diamond, although his status as an environmental determinist is debated.
Biological determinism is the idea that all behavior, belief, and desire are fixed by our genetic endowment. There are other theses on determinism, including cultural determinism and the narrower concept of psychological determinism. Combinations and syntheses of determinist theses, e.g. bio-environmental determinism, are even more common. Addiction Specialist Dr. Drew Pinski relates addiction to biological determinism:
"Absolutely. It's a complex disorder, but it clearly has a genetic basis. In fact, in the definition of the disease, we consider genetics absolutely a crucial piece of the definition. So the definition as stated in a consensus conference that was published in the early '90s, it's a genetic disorder with a biological basis. The hallmark is the progressive use in the face of adverse consequence, and then finally denial."
Theological determinism is the thesis that there is a God who determines all that humans will do, either by knowing their actions in advance, via some form of omniscience or by decreeing their actions in advance. The problem of free will, in this context, is the problem of how our actions can be free, if there is a being who has determined them for us ahead of time.
In the story of the Indra's Net, the light that streams back and forth throughout the display is the analogy of karma. (Note that in popular Western usage, the word "karma" often refers to the concept of past good or bad actions resulting in like consequences.) In the Eastern context "Karma" refers to an action, or, more specifically, to an intentional action, and the Buddhist theory holds that every karma (every intentional action) will bear karmic fruit (produce an effect somewhere down the line). Volitional acts drive the universe. The consequences of this view often confound our ordinary expectations.
A shifting flow of probabilities for futures lies at the heart of theories associated with the Yi Jing (or I Ching, the Book of Changes). Probabilities take the center of the stage away from things and people. A kind of "divine" volition sets the fundamental rules for the working out of probabilities in the universe, and human volitions are always a factor in the ways that humans can deal with the real world situations one encounters. If one's situation in life is surfing on a tsunami, one still has some range of choices even in that situation. One person might give up, and another person might choose to struggle and perhaps to survive. The Yi Jing mentality is much closer to the mentality of quantum physics than to that of classical physics, and also finds parallelism in voluntarist or Existentialist ideas of taking one's life as one's project.
The followers of the philosopher Mozi made some early discoveries in optics and other areas of physics, ideas that were consonant with deterministic ideas.
Whether or not it is all-encompassing in so doing, Newtonian mechanics deals only with caused events, e.g.: If an object begins in a known position and is hit dead on by an object with some known velocity, then it will be pushed straight toward another predictable point. If it goes somewhere else, the Newtonians argue, one must question one's measurements of the original position of the object, the exact direction of the striking object, gravitational or other fields that were inadvertently ignored, etc. Then, they maintain, repeated experiments and improvements in accuracy will always bring one's observations closer to the theoretically predicted results. When dealing with situations on an ordinary human scale, Newtonian physics has been so enormously successful that it has no competition. But it fails spectacularly as velocities become some substantial fraction of the speed of light and when interactions at the atomic scale are studied. Before the discovery of quantum effects and other challenges to Newtonian physics, "uncertainty" was always a term that applied to the accuracy of human knowledge about causes and effects, and not to the causes and effects themselves.
A number of positions can be delineated:
In emergentist or generative philosophy of cognitive sciences and evolutionary psychology, free will does not exist. However an illusion of free will is experienced due to the generation of infinite behaviour from the interaction of finite-deterministic set of rules and parameters. Thus the unpredictability of the emerging behaviour from deterministic processes leads to a perception of free will, even though free will as an ontological entity does not exist.
As an illustration, the strategy board-games chess and Go have rigorous rules in which no information (such as cards' face-values) is hidden from either player and no random events (such as dice-rolling) happen within the game. Yet, chess and especially Go with its extremely simple deterministic rules, can still have an extremely large number of unpredictable moves. By analogy, emergentists or generativists suggest that the experience of free will emerges from the interaction of finite rules and deterministic parameters that generate infinite and unpredictable behaviour. Yet, if all these events were accounted for, and there were a known way to evaluate these events, the seemingly unpredictable behaviour would become predictable.
Dynamical-evolutionary psychology, cellular automata and the generative sciences, model emergent processes of social behaviour on this philosophy, showing the experience of free will as essentially a gift of ignorance or as a product of incomplete information.
Many mathematical models are deterministic. This is true of most models involving differential equations (notably, those measuring rate of change over time). Mathematical models that are not deterministic because they involve randomness are called stochastic. Because of sensitive dependence on initial conditions, some deterministic models may appear to behave non-deterministically; in such cases, a deterministic interpretation of the model may not be useful due to numerical instability and a finite amount of precision in measurement. Such considerations can motivate the consideration of a stochastic model when the underlying system is accurately modeled in the abstract by deterministic equations.
At atomic scales the paths of objects can only be predicted in a probabilistic way. The paths may not be exactly specified in a full quantum description of the particles; "path" is a classical concept which quantum particles do not exactly possess. The probability arises from the measurement of the perceived path of the particle. In some cases, a quantum particle may trace an exact path, and the probability of finding the particles in that path is one. The quantum development is at least as predictable as the classical motion, but it describes wave functions that cannot be easily expressed in ordinary language. In double-slit experiments, light is fired singly through a double-slit apparatus at a distant screen and does not arrive at a single point, nor do the photons arrive in a scattered pattern analogous to bullets fired by a fixed gun at a distant target. Instead, the light arrives in varying concentrations at widely separated points, and the distribution of its collisions can be calculated reliably. In that sense the behavior of light in this apparatus is deterministic, but there is no way to predict where in the resulting interference pattern an individual photon will make its contribution (see Heisenberg Uncertainty Principle).
Some have argued that, in addition to the conditions humans can observe and the laws we can deduce, there are hidden factors or "hidden variables" that determine absolutely in which order photons reach the detector screen. They argue that the course of the universe is absolutely determined, but that humans are screened from knowledge of the determinative factors. So, they say, it only appears that things proceed in a merely probabilistically-determinative way. In actuality, they proceed in an absolutely deterministic way. Although matters are still subject to some measure of dispute, quantum mechanics makes statistical predictions which would be violated if some local hidden variables existed. There have been a number of experiments to verify those predictions, and so far they do not appear to be violated, though many physicists believe better experiments are needed to conclusively settle the question. (See Bell test experiments.) It is possible, however, to augment quantum mechanics with non-local hidden variables to achieve a deterministic theory that is in agreement with experiment. An example is the Bohm interpretation of quantum mechanics.
On the macro scale it can matter very much whether a bullet arrives at a certain point at a certain time, as snipers are well aware; there are analogous quantum events that have macro- as well as quantum-level consequences. It is easy to contrive situations in which the arrival of an electron at a screen at a certain point and time would trigger one event and its arrival at another point would trigger an entirely different event. (See Schrödinger's cat.)
Even before the laws of quantum mechanics were fully developed, the phenomenon of radioactivity posed a challenge to determinism. A gram of uranium-238, a commonly occurring radioactive substance, contains some 2.5 x 1021 atoms. By all tests known to science these atoms are identical and indistinguishable. Yet about 12600 times a second one of the atoms in that gram will decay, giving off an alpha particle. This decay does not depend on external stimulus and no extant theory of physics predicts when any given atom will decay, with realistically obtainable knowledge. The uranium found on earth is thought to have been synthesized during a supernova explosion that occurred roughly 5 billion years ago. For determinism to hold, every uranium atom must contain some internal "clock" that specifies the exact time it will decay. And somehow the laws of physics must specify exactly how those clocks were set as each uranium atom was formed during the supernova collapse.
Exposure to alpha radiation can cause cancer. For this to happen, at some point a specific alpha particle must alter some chemical reaction in a cell in a way that results in a mutation. Since molecules are in constant thermal motion, the exact timing of the radioactive decay that produced the fatal alpha particle matters. If probabilistically determined events do have an impact on the macro events -- such as when a person who could have been historically important dies in youth of a cancer caused by a random mutation -- then the course of history is not determined from the dawn of time.
So quantum mechanics is deterministic, provided that one accepts the wave function itself as reality (rather than as probability of classical coordinates). Since we have no practical way of knowing the exact magnitudes, and especially the phases, in a full quantum mechanical description of the causes of an observable event, this turns out to be philosophically similar to the "hidden variable" doctrine.
According to some, quantum mechanics is more strongly ordered than Classical Mechanics, because while Classical Mechanics is chaotic, quantum mechanics is not. For example, the classical problem of three bodies under a force such as gravity is not integrable, while the quantum mechanical three body problem is tractable and integrable, using the Faddeev Equations. That is, the quantum mechanical problem can always be solved to a given accuracy with a large enough computer of predetermined precision, while the classical problem may require arbitrarily high precision, depending on the details of the motion. This does not mean that quantum mechanics describes the world as more deterministic, unless one already considers the wave function to be the true reality. Even so, this does not get rid of the probabilities, because we can't do anything without using classical descriptions, but it assigns the probabilities to the classical approximation, rather than to the quantum reality.
Asserting that quantum mechanics is deterministic by treating the wave function itself as reality implies a single wave function for the entire universe, starting at the big bang. Such a "wave function of everything" would carry the probabilities of not just the world we know, but every other possible world that could have evolved from the big bang. For example, large voids in the distributions of galaxies are believed by many cosmologists to have originated in quantum fluctuations during the big bang. (See cosmic inflation and primordial fluctuations.) If so, the "wave function of everything" would carry the possibility that the region where our Milky Way galaxy is located could have been a void and the Earth never existed at all. (See large-scale structure of the cosmos.)
Assume: All events have causes, and their causes are all prior events. There is no cycle of events such that an event (possibly indirectly) causes itself.
The picture this gives us is that Event AN is preceded by AN-1, which is preceded by AN-2, and so forth.
Under these assumptions, two possibilities seem clear, and both of them question the validity of the original assumptions:
Under this analysis the original assumption must have something wrong with it. It can be fixed by admitting one exception, a creation event (either the creation of the original event or events, or the creation of the infinite series of events) that is itself not a caused event in the sense of the word "caused" used in the formulation of the original assumption. Some agency, which many systems of thought call God, creates space, time, and the entities found in the universe by means of some process that is analogous to causation but is not causation as we know it. This solution to the original difficulty has led people to question whether there is any reason for there only being one divine quasi-causal act, whether there have not been a number of events that have occurred outside the ordinary sequence of events, events that may be called miracles. Another possibility is that the "last event" loops back to the "first event" causing an infinite loop. If you were to call the Big Bang the first event, you would see the end of the Universe as the "last event". In theory, the end of the Universe would be the cause of the beginning of the Universe. You would be left with an infinite loop of time with no real beginning or end. This theory eliminates the need for a first cause, but does not explain why there should be a loop in time.
Immanuel Kant carried forth this idea of Leibniz in his idea of transcendental relations, and as a result, this had profound effects on later philosophical attempts to sort these issues out. His most influential immediate successor, a strong critic whose ideas were yet strongly influenced by Kant, was Edmund Husserl, the developer of the school of philosophy called phenomenology. But the central concern of that school was to elucidate not physics but the grounding of information that physicists and others regard as empirical. In an indirect way, this train of investigation appears to have contributed much to the philosophy of science called logical positivism and particularly to the thought of members of the Vienna Circle, all of which have had much to say, at least indirectly, about ideas of determinism.
decision rules and emergent social norms. Psychological Review, 110, 3–28