| Thinking hardly|
or hardly thinking?
|Major trains of thought|
|The good, the bad|
and the brain fart
|Come to think of it|
Reductionism is the philosophical position that a complex phenomenon can be described ultimately by the component pieces that make up that phenomenon. Reductionism can be applied to almost anything, whether it is a physical system, a process, a thought, or a living creature. Many argue that the scientific method relies heavily on reductionism, and science's ability to accurately model reality is linked to how much it can be reduced. Others have argued that certain systems demonstrate emergent properties that are above and beyond the component pieces of the system. Many attempts are being developed to figure out a way to test for the existence of and ultimately rigorously study these kinds of phenomena.
Ontological vs. methodological reductionism
Two forms of reductionism are often contrasted. Methodological reductionism refers to the use of a methodology that seeks to describe or explain a phenomenon in terms of its constituent pieces. Ontological reductionism makes the stronger, metaphysical claim that the phenomenon itself doesn't exist, but only its constituent parts do. This is sometimes referred to as "eliminativism."
Unification of science by means of reductionism
“”Math is really logic. Logic is really philosophy. Philosophy is really psychology. Psychology is really biology. Biology is really Chemistry. Chemistry is really physics. Physics is really math.
Various schemes to subsume what are sometimes known as the "special sciences" into a "fundamental" or "general science" have been proposed throughout the history of science. The search for a "theory of everything" has been construed by some as a potential discovery that would unify and reduce all science to physics. This is pithily summed up by Ernest Rutherford's quip that "All science is either physics or stamp collecting." This position is often ascribed to the "unity of science" movement associated with logical positivism, though not all the scientists and philosophers in this tradition held to a strict version of it. Others have advocated collapsing the social sciences and humanities into biology, using evolution as unifying theory. (Or sometimes, the weaker claim that all the special sciences should be done using an evolutionary or biological approach.) This notion was popularized by Edward O. Wilson in his book Consilience: The Unity of Knowledge. In Darwin's Dangerous Idea, Daniel Dennett uses evolution as a unifying theory but takes a different approach by re-conceptualizing natural selection as an algorithmic process that can be applied to all fields of knowledge.
Arguments against reductionism
Due to the success of reductionist programs in science, it has often been taken that (by induction) all scientifically-oriented research ought to be reductionist in nature. A number of arguments have been made against this line of thinking, proposing methodologies from ones that fully integrate reductionism but constrain its applicability to some degree to ones that reject reductionism entirely.
The majority of states of matter in quantum theory have holistic features, but these can be analysed by studying correlations of repeated measurements on the components. Thus although the world actually is holistic, it's not so holistic that reductionist techniques cannot be applied 
Anti-reductionism and holism
Anti-reductionist arguments are often associated with holism, although this is not necessarily the case. The term "holism" was originally coined by Jan Smuts to refer to the co-evolution between parts and wholes. He defined "wholism" as the concept that the whole is more than the sum of its parts.
In philosophy of mind, Jerry Fodor argued against reductionism (extending an argument made by Hilary Putnam) on the grounds of multiple realizability, i.e., that multiple physical kinds may underlie a single mental state. But Fodor has also argued against holism, claiming that it would make scientific psychology impossible because it would prevent any generalizations being made about mental states.
Another common angle from which to attack reductionism is to point out failed attempts to reduce certain special sciences. In biology, this usually involves arguing from the lack of a reductive account of evolution or genetics in terms of molecular biology. In the behavioral and cognitive sciences, the lack of a reductive account of the "hard problem" of consciousness is used as ammo for anti-reductionist arguments. (Though some deny that the hard problem exists.)
"Reductionism" is sometimes used as an epithet in anti-science rhetoric. For example, a common accusation from alternative medicine practitioners is that real doctors practice reductionism, and refuse to consider the "whole." This is entirely untrue; doctors look at all possible vectors of disease when diagnosing a patient, including the possibility of psychosomatic illness.[note 1] Ironically, practitioners such as chiropractors think you can reduce a diagnosis to the spine only. (When your only tool's a hammer...)
Quite often, this comes down to a failure to distinguish between ontological and methodological reductionism.
- Reductionism, Internet Encyclopedia of Philosophy
- Reduction, On Philosophy
- Reductionism, Anti-Reductionism, and Supervenience, Philosophy of Science notes, Drury University
- Thomas Nagel. Reductionism and Antireductionism. The Limits of Reductionism in Biology, 1998 Novartis Foundation symposium.
- John Cleese on reductionism
- What's a good ending for 'Biology is really chemistry. Chemistry is really physics. Physics is really math. Math is really hard'? - Quora
- Undisciplined Science, Brian Hayes, American Scientist
- See The Unity of Science in the SEP
- See the Wikipedia article on Consilience (book).
- See the Wikipedia article on Darwin's Dangerous Idea.
- Quantum Theory from First Principles: An Informational Approach, Giacomo D'Ariano et al
- Smuts' Holism and Evolution, Dave Marsay
- Jerry Fodor. Special Sciences (Or: The Disunity of Science as a Working Hypothesis. Synthese, Vol. 28, No. 2 (Oct., 1974), pp. 97-115
- See also SEP's entry for Multiple Realizability
- Ernest Lepore and Jerry Fodor. Precis of Holism: A Shopper's Guide. Philosophy and Phenomenological Research Vol. 53, No. 3 (Sep., 1993), pp. 637-640
- See SEP's entry for Reductionism in Biology
- See the IEP's entry for The Hard Problem of Consciousness.