In philosophy, reduction is the process by which one object, property, concept, theory, etc., is shown to be explicable in terms of another, lower level, concept, object, property, etc. For example, we say that physical properties such as the boiling point of a substance are reducible to that substance’s atomic properties, because we are able to explain why a liquid boils at a certain temperature using only the properties of its constituent atoms. Thus we might also describe reduction as a process analogous to absorption, by which one theory (or concept, or property, and so on) is wholly subsumed under another.
In science, such reduction is generally desirable, because it explains why and how the thing which is being reduced exists, and because it promotes conceptual and theoretical economy. Reducing chemical properties to properties of atoms thus explains why certain substances have the chemical properties that they do, and integrates these properties into a single explanatory framework, that of atomic structure.
Reductionism may therefore be divided into three general areas – methodological, theoretical, and ontological – and reduction (the process) into two – theoretical and ontological.
Types of reductionism
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.)
Types of reduction
The 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.
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