Reductionism refers to several related but different philosophical positions regarding the connections between phenomena, or theories, "reducing" one to another, usually considered "simpler" or more "basic". The Oxford Companion to Philosophy suggests that it is "one of the most used and abused terms in the philosophical lexicon" and suggests a three part division:
Ontological reductionism: a belief that the whole of reality consists of a minimal number of parts
Methodological reductionism: the scientific attempt to provide explanation in terms of ever smaller entities
Theory reductionism: the suggestion that a newer theory does not replace or absorb the old, but reduces it to more basic terms. Theory reduction itself is divisible into three: translation, derivation and explanation.
Reductionism can be applied to objects, phenomena, explanations, theories, and meanings.
In the sciences, application of methodological reductionism attempts explanation of entire systems in terms of their individual, constituent parts and their interactions. Thomas Nagel speaks of psychophysical reductionism (the attempted reduction of psychological phenomena to physics and chemistry), as do others and physico-chemical reductionism (the attempted reduction of biology to physics and chemistry), again as do others. In a very simplified and sometimes contested form, such reductionism is said to imply that a system is nothing but the sum of its parts. . . . more