1 a theory that all complex systems can be completely understood in terms of their components
2 the analysis of complex things into simpler constituents
Reductionism can either mean (a) an approach to understanding the nature of complex things by reducing them to the interactions of their parts, or to simpler or more fundamental things or (b) a philosophical position that a complex system is nothing but the sum of its parts, and that an account of it can be reduced to accounts of individual constituents. This can be said of objects, phenomena, explanations, theories, and meanings.
Reductionism is strongly related to a certain perspective on causality. In a reductionist framework, phenomena that can be explained completely in terms of other, more fundamental phenomena, are called epiphenomena. Often there is an implication that the epiphenomenon exerts no causal agency on the fundamental phenomena that explain it.
HistoryReductionism originated with the earliest philosophy. Thales of Miletus believed that the world was water. Anaximander of Miletus disagreed and stated that the world was apeiron. Anaximander's pupil Anaximenes claimed that the world was air. Heraclitus of Ephesus declared that "this world-order [the same of all] did none of gods or men make, but it always was and is and shall be: an ever-living fire, kindling in measures and going out in measures" according to the Logos.
Types of reductionismThe distinction between the processes of theoretical and ontological reduction is equally important. Theoretical reduction is the process by which one theory is absorbed into another; for example, both Kepler's laws of the motion of the planets and Galileo’s theories of motion worked out for terrestrial objects are reducible to Newtonian theories of mechanics, because all the explanatory power of the former are contained within the latter. Furthermore, the reduction is considered to be beneficial because Newtonian mechanics is a more general theory—that is, it explains more events than Galileo's or Kepler's. Theoretical reduction, therefore, is the reduction of one explanation or theory to another—that is, it is the absorption of one of our ideas about a particular thing into another idea.
Methodological reductionism is the position that the best scientific strategy is to attempt to reduce explanations to the smallest possible entities. Methodological reductionism would thus hold that the atomic explanation of a substance’s boiling point is preferable to the chemical explanation, and that an explanation based on even smaller particles (quarks, perhaps) would be even better.
Theoretical reductionism is the position that all scientific theories either can or should be reduced to a single super-theory through the process of theoretical reduction.
Finally, ontological reductionism is the belief that reality is composed of a minimum number of kinds of entities or substances. This claim is usually metaphysical, and is most commonly a form of monism, in effect claiming that all objects, properties and events are reducible to a single substance. (A dualist who is an ontological reductionist would presumably believe that everything is reducible to one of two substances.)
Reductionism and science
Reductionist thinking and methods are the basis for many of the well-developed areas of modern science, including much of physics, chemistry and cell biology. Classical mechanics in particular is seen as a reductionist framework, and statistical mechanics can be viewed as a reconciliation of macroscopic thermodynamic laws with the reductionist approach of explaining macroscopic properties in terms of microscopic components.
In science, reductionism can be understood to imply that certain fields of study are based on areas that study smaller spatial scales or organizational units. While it is commonly accepted that most aspects of chemistry are based on physics, and similarly many aspects of microbiology are based on chemistry, such statements become controversial when one considers larger-scale fields. For example, claims that sociology is based on psychology, or that economics is based on sociology and psychology would be met with reservations. These claims are difficult to substantiate even though there are clear connections between these fields (for instance, most would agree that psychology can impact and inform economics.) The limit of reductionism's usefulness stems from emergent properties of complex systems which are more common at certain levels of organization. For example, certain aspects of evolutionary psychology and sociobiology are rejected by some who claim that complex systems are inherently irreducible and that a holistic approach is needed to understand them.
Daniel Dennett defends scientific reductionism, which he says is really little more than materialism, by making a distinction between this and what he calls "Greedy reductionism": the idea that every explanation in every field of science should be reduced all the way down to particle physics or string theory. Greedy reductionism, he says, deserves some of the criticism that has been heaped on reductionism in general because the lowest-level explanation of a phenomenon, even if it exists, is not always the best way to understand or explain it.
Some strong reductionists believe that the behavioral sciences should become "genuine" scientific disciplines by being based on genetic biology, and on the systematic study of culture (cf. Dawkins's concept of memes). In his book The Blind Watchmaker, Richard Dawkins introduced the term "hierarchical reductionism" to describe the view that complex systems can be described with a hierarchy of organizations, each of which can only be described in terms of objects one level down in the hierarchy. He provides the example of a computer, which under hierarchical reductionism can be explained well in terms of the operation of hard drives, processors, and memory, but not on the level of AND or NOR gates, or on the even lower level of electrons in a semiconductor medium.
Both Dennett and Steven Pinker argue that too many people who are opposed to science use the words "reductionism" and "reductionist" less to make coherent claims about science than to convey a general distaste for the endeavor. Furthermore, these opponents often use the words in a rather slippery way, to refer to whatever they dislike most about science. Dennett suggests that critics of reductionism may be searching for a way of salvaging some sense of a higher purpose to life, in the form of some kind of non-material / supernatural intervention. Dennett terms such aspirations "skyhooks," in contrast to the "cranes" that reductionism uses to build its understanding of the universe from solid ground.
Others, including the ecologist Robert Ulanowicz, argues that inappropriate use of reductionism limits our understanding of complex systems. He argues that science must develop techniques to study ways in which larger scales of organization influence smaller ones, and also ways in which feedback loops create structure at a given level, independently of details at a lower level of organization. He advocates (and uses) information theory as a framework to study propensities in natural systems. Ulanowicz attributes these criticisms of reductionism to the philosopher Karl Popper and biologist Robert Rosen.
Reductionism in mathematics
In mathematics, reductionism can be interpreted as the philosophy that all mathematics can (or ought to) be built off a common foundation, which is usually axiomatic set theory. Ernst Zermelo was one of the major advocates of such a view, and he was also responsible for the development of much of axiomatic set theory. It has been argued that the generally accepted method of justifying mathematical axioms by their usefulness in common practice can potentially undermine Zermelo's reductionist program.
As an alternative to set theory, others have argued for category theory as a foundation for certain aspects of mathematics.
Ontological reductionismOntological reductionism is a philosophy or belief that everything that exists is made from a small number of basic substances that behave in regular ways (compare to monism). Ontological reductionism denies the idea of ontological emergence, and claims that emergence is an epistemological phenomenon that only exists through analysis or description of a system, and does not exist on a fundamental level.
Ontological reductionism takes two different forms: Token ontological reductionism is the idea that every item that exists is a sum item. For perceivable items, it says that every perceivable item is a sum of items at a smaller level of complexity. Type ontological reductionism is the idea that every type of item is a sum (of typically less complex) type(s) of item(s). For perceivable types of item, it says that every perceivable type of item is a sum of types of items at a lower level of complexity. Token ontological reduction of biological things to chemical things is generally accepted. Type ontological reduction of biological things to chemical things is often rejected.
Reductionism in linguisticsLinguistic reductionism is the idea that everything can be described in a language with a limited number of core concepts, and combinations of those concepts. (See Basic English and the constructed language Toki Pona).
Limits of reductionism
A contrast to the reductionist approach is holism or emergentism. Holism recognizes the idea that things can have properties as a whole that are not explainable from the sum of their parts (emergent properties). The principle of holism was concisely summarized by Aristotle in the Metaphysics: "The whole is more than the sum of its parts".
The term Greedy reductionism, coined by Daniel Dennett, is used to criticize inappropriate use of reductionism. Other authors use different language when describing the same thing.
The concept of downward causation poses an alternative to reductionism within philosophy. This view is developed and explored by Peter Bøgh Andersen, Claus Emmeche, Niels Ole Finnemann, and Peder Voetmann Christiansen, among others. These philosophers explore ways in which one can talk about phenomena at a larger-scale level of organization exerting causal influence on a smaller-scale level, and find that some, but not all proposed types of downward causation are compatible with science. In particular, they find that constraint is one way in which downward causation can operate. The notion of causality as constraint has also been explored as a way to shed light on scientific concepts such as self-organization, natural selection, adaptation, and control.
Phenomena such as emergence and work within the field of complex systems theory pose limits to reductionism. Stuart Kauffman is one of the advocates of this viewpoint. Emergence is strongly related to nonlinearity. The limits of the application of reductionism become especially evident at levels of organization with higher amounts of complexity, including culture, neural networks, ecosystems, and other systems formed from assemblies of large numbers of interacting components. Symmetry breaking is an example of an emergent phenomenon. Nobel laureate P.W.Anderson used this idea in his famous paper in Science in 1972, 'More is different' to expose some of the limitations of reductionism. The limitation of reductionism was explained as follows. The sciences can be arranged roughly linearly in a hierarchy as particle physics, many body physics, chemistry, molecular biology, cellular biology, ..., physiology, psychology and social sciences. The elementary entities of one science obeys the laws of the science that precedes it in the above hierarchy. But, this does not imply that one science is just an applied version of the science that precedes it. Quoting from the article, "At each stage, entirely new laws, concepts and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one. Psychology is not applied biology nor is biology applied chemistry."
Sven Erik Jorgensen, an ecologist, lays out both theoretical and practical arguments for a holistic approach in certain areas of science, especially ecology. He argues that many systems are so complex that it will not ever be possible to describe all their details. Drawing an analogy to the Heisenberg uncertainty principle in physics, he argues that many interesting and relevant ecological phenomena cannot be replicated in laboratory conditions, and thus cannot be measured or observed without influencing and changing the system in some way. He also points to the importance of interconnectedness in biological systems. His viewpoint is that science can only progress by outlining what questions are unanswerable and by using models that do not attempt to explain everything in terms of smaller hierarchical levels of organization, but instead model them on the scale of the system itself, taking into account some (but not all) factors from levels both higher and lower in the hierarchy.
Disciplines such as cybernetics and systems theory strongly embrace a non-reductionist view of science, sometimes going as far as explaining phenomena at a given level of hierarchy in terms of phenomena at a higher level, in a sense, the opposite of a reductionist approach..
In decision theory
In decision theory, a nonlinear utility function for a quantity such as money can create a situation in which all relevant decisions to be made in a given time period must to be considered simultaneously in order to maximize utility, if all relevant decisions act on utility only through this quantity. In such a situation, the optimal choice for a given decision depends on the possible outcomes of all other decisions, including those which may have no causal relationship to the decision at hand. Breaking such a problem apart into individual decisions and optimizing each smaller decision can lead to drastically sub-optimal decisions. Such nonlinear utility functions for money are used in economics and are necessary in order to satisfy reasonable assumptions about rational behavior. Such decision making situations are the norm, rather than the exception, in many business settings.
Some religious belief or doctrine assigns supernatural original causes to phenomena. In this context, even if a given system appears to operate by causes and effects that can be explained within a strict reductionist framework, belief or doctrine might hold that its true genesis and placement within larger (and typically unknown) systems is bound up with an intelligence or consciousness that is beyond normal or uninvited human perception. Some such beliefs constitute a form of teleology, a perspective which is generally in conflict with reductionism.
Benefits of reduction
An ontological reduction reduces the number of ontological primitives that exist within our ontology. Philosophers welcome this, because every ontological primitive demands a special explanation for its existence. If we maintain that life is not a physical property, for example, then we must give a separate explanation of why some objects possess it and why others do not. This is more often than not a daunting task, and such explanations often have the flavor of ad hoc contrivances or deus ex machina. Also, since every ontological primitive must be acknowledged as one of the fundamental principles of the natural world, we must also account for why this element in particular should be considered one of those underlying principles. (To return to an earlier example, it would be extremely difficult to explain why planets are so fundamental that special laws of motion should apply to them.) This is often extremely hard to do, especially in the face of our strong preference for simple explanations. Pursuing ontological reduction thus serves to unify and simplify our ontology, while guarding against needless multiplication of entities in the process.
At the same time, the requirements for satisfactorily showing that one thing is reducible to another are extremely steep. First and foremost, all features of the original property or object must be accounted for. For example, lightning would not be reducible to the electrical activity of air molecules if the reduction explained why lightning is deadly, but not why it always seeks the highest point to strike. Our preference for simple and unified explanations is a strong force for reductionism, but our demand that all relevant phenomena be accounted for is at least as strong a force against it.
Alternatives to reductionism
In recent years, the development of systems thinking has provided methods for tackling issues in a holistic rather than a reductionist way, and many scientists approach their work in a holistic paradigm. When the terms are used in a scientific context, holism and reductionism refer primarily to what sorts of models or theories offer valid explanations of the natural world; the scientific method of falsifying hypotheses, checking empirical data against theory, is largely unchanged, but the approach guides which theories are considered. The conflict between reductionism and holism in science is not universal--it usually centers on whether or not a holistic or reductionist approach is appropriate in the context of studying a specific system or phenomenon.
In many cases (such as the kinetic theory of gases), given a good understanding of the components of the system, one can predict all the important properties of the system as a whole. In other cases, trying to do this leads to a fallacy of composition. In those systems, emergent properties of the system are almost impossible to predict from knowledge of the parts of the system. Complexity theory studies such systems.
- Dawkins, R. (1976) The Selfish Gene. Oxford University Press; 2nd edition, December 1989 ISBN 0-19-217773-7.
- Descartes (1637) Discourses Part V
- Dupre, J. (1993) The Disorder of Things. Harvard University Press.
- Jones, Richard H. Reductionism: Analysis and the Fullness of Reality. Bucknell University Press. (For the general reader.)
- Nagel, E. (1961) The Structure of Science. New York.
- Ruse, M. (1988) Philosophy of Biology. Albany, NY.
- Dennett, Daniel. (1995) Darwin's Dangerous Idea. Simon & Schuster. ISBN 0-684-82471-X.
- Fritjof Capra. (1982) The Turning Point.
- Alexander Rosenberg (2006) Darwinian Reductionism or How to Stop Worrying and Love Molecular Biology. University of Chicago Press.
- Steven Pinker (2002) The Blank Slate: The Modern Denial of Human Nature. Viking Penguin.
- Steven Weinberg (2002) describes what he terms the culture war among physicists in his review of A New Kind of Science
- Eric Scerri The reduction of chemistry to physics has become a central aspect of the philosophy of chemistry. See several articles by this author.
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