Equifinality is the principle that in open systems a given end state can be reached by many potential means. The term and concept is due to Hans Driesch, the developmental biologist, later applied by Ludwig von Bertalanffy, the founder of general systems theory. They prefer this term, in contrast to "goal", in describing complex systems' similar or convergent behavior. It emphasizes that the same end state may be achieved via many different paths or trajectories. In closed systems, a direct cause-and-effect relationship exists between the initial condition and the final state of the system: When a computer's 'on' switch is pushed, the system powers up. Open systems (such as biological and social systems), however, operate quite differently. The idea of equifinality suggests that similar results may be achieved with different initial conditions and in many different ways. This phenomenon has also been referred to as isotelesis (Greek: ἴσος /isos/ "equal", τέλεσις /telesis/ "the intelligent direction of effort toward the achievement of an end.") when in games involving superrationality.
In business, equifinality implies that firms may establish similar competitive advantages based on substantially different competencies.
In psychology, equifinality refers to how different early experiences in life (e.g., parental divorce, physical abuse, parental substance abuse) can lead to similar outcomes (e.g., childhood depression). In other words, there are many different early experiences that can lead to the same psychological disorder.
In archaeology, equifinality refers to how different historical processes may lead to a similar outcome or social formation. For example, the development of agriculture or the bow and arrow occurred independently in many different areas of the world, yet for different reasons and through different historical trajectories. This highlights that generalizations based on cross-cultural comparisons cannot be made uncritically.
In geomorphology, the term equifinality indicates that similar landforms might arise as a result of quite different sets of processes.
In environmental modeling studies, and especially in hydrological modeling, two models are equifinal if they lead to an equally acceptable or behavioral representation of the observed natural processes. It is a key concept to assess how uncertain hydrological predictions are.
- GLUE – Generalized Likelihood Uncertainty Estimation (when modeling environmental systems there are many different model structures and parameter sets that may be behavioural or acceptable in reproducing the behaviour of that system)
- TMTOWTDI – Computer programming maxim: "there is more than one way to do it"
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