Biological reductionism

Reductionism refers to several related philosophical ideas regarding the associations between phenomena which can be described in terms of other phenomena, the latter of which are considered in some manner simpler or more fundamental.

The Oxford Companion to Philosophy suggests that reductionism is "one of the most used and abused terms in the philosophical lexicon" and suggests a three part division:

Reductionism can be applied to any phenomenon, including objects, explanations, theories, and meanings.

For the sciences, application of methodological reductionism attempts explanation of entire systems in terms of their individual, constituent parts and their interactions. For example, the temperature of a gas is reduced to nothing but the average kinetic energy of its molecules in motion. 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. However, a more nuanced opinion is that a system is composed entirely of its parts, but the system will have features that none of the parts have. "The point of mechanistic explanations is usually showing how the higher level features arise from the parts."

Other definitions are used by other authors. For example, what John Polkinghorne terms conceptual or epistemological reductionism is the definition provided by Simon Blackburn and by Jaegwon Kim: that form of reductionism concerning a program of replacing the facts or entities entering statements claimed to be true in one type of discourse with other facts or entities from another type, thereby providing a relationship between them. Such an association is provided where the same idea can be expressed by "levels" of explanation, with higher levels reducible if need be to lower levels. This use of levels of understanding in part expresses our human limitations in remembering detail. However, "most philosophers would insist that our role in conceptualizing reality [our need for an hierarchy of "levels" of understanding] does not change the fact that different levels of organization in reality do have different properties."

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