Overdetermination occurs when a single-observed effect is determined by multiple causes, any one of which alone would be conceivably sufficient to account for ("determine") the effect. The term "overdetermination" () was used by Sigmund Freud as a key concept in his psychoanalysis, and later by Louis Althusser.
In the philosophy of science, the concept of overdetermination has been used to describe a situation in which there are more causes present than are necessary to cause an effect. Overdetermination here is in contrast to underdetermination, when the number or strength of causes is insufficient.
Freud and psychoanalysis
Freud wrote in The Interpretation of Dreams that many features of dreams were usually "overdetermined," in that they were caused by multiple factors in the life of the dreamer, from the "residue of the day" (superficial memories of recent life) to deeply repressed traumas and unconscious wishes, these being "potent thoughts". Freud favored interpretations which accounted for such features not only once, but many times, in the context of various levels and complexes of the dreamer's psyche.
The concept was later borrowed for a variety of other realms of thought.
Richards and literature
The New Critic I. A. Richards appealed to Freud's idea of overdetermination while explaining why what Richards called a 'context theorem of meaning' showed the importance of ambiguity in rhetoric, the philosophy of language, and literary criticism:
Althusser and structuralist Marxism
The Marxist philosopher Louis Althusser imported the concept into Marxist political theory in an influential essay, "Contradiction and overdetermination." Drawing from both Freud and Mao Zedong, Althusser used the idea of overdetermination as a way of thinking about the multiple, often opposed, forces active at once in any political situation, without falling into an overly simple idea of these forces being simply "contradictory." Brewster, in Althusser et al.'s Reading Capital defines overdetermination as such:
"Althusser uses [overdetermination] to describe the effects of the contradictions in each practice constituting the social formation on the social formation as a whole, and hence back on each practice and each contradiction, defining the pattern of dominance and subordination, antagonism and non-antagonism of the contradictions in the structure in dominance at any given historical moment. More precisely, the overdetermination of a contradiction is the reflection in it of its conditions of existence within the complex whole, that is, of the other contradictions in the complex whole, in other words its uneven development."
An instance of a popular riot calling for revolution could exemplify overdetermination. The event has to it, in capitalist culture, an over-application (determination) of agitation. The determinant contradictions (the reasons for popular revolt) are not addressed and so their great mass is "displaced" onto the singular event.
In analytic philosophy
In contemporary analytic philosophy an event or state of affairs is said to be overdetermined if it has two or more distinct, sufficient causes. In philosophy of mind, the famous case of overdetermination is called mental-physical causal overdetermination. If we accept that a mental state (M) is realized by a physical state (P). And M can cause another mental state (M*) or another physical state (P*). Then, nomologically speaking, P can cause M* or P* too. In this way, M* or P* is both determined by M and P. In other words, both M* and P* are overdetermined. Since either M or P is sufficient for M* or P*, the problem of mental-physical causal overdetermination is the causal redundancy.
Whereas there may unproblematically be recognised many different necessary conditions of the event's occurrence, no two distinct events may lay claim to be sufficient conditions, since this would lead to overdetermination. A much used example is that of firing squads, the members of which simultaneously firing at and 'killing' their targets. Apparently, no one member can be said to have caused the victims' deaths, since they would have been killed anyway. Another example is that Billy and Suzy each throw a rock through a window, and either rock alone could have shattered the window. In this case, similar to the example of firing squads, Billy and Suzy together shatter the window and the result is not overdetermined. Or, we can say, even if these two examples are a kind of overdetermination, this kind of overdetermination is benign.