Holism and reductionism refer to two often competing approaches for understanding and explaining phenomena in the world. The distinction is most relevant for understanding complex physical, biological, social, economic, and political systems. Reductionism is view that such systems can best be understood by breaking them up into progressively smaller component parts, analysing each part in isolation, and then attempting to assemble a picture or model of how the parts work together. Holism is the contrasting view that such an approach is inadequate for full understanding because complex systems exhibit behaviours and possess properties that cannot be discerned from mere study of their component parts, and which can only be revealed by study of the system as a unified whole.
Reductionist approaches are most common in the sciences, while disciplines in the humanities are more likely to use a combination of holistic and reductionist methodologies. One example of contrasting approaches can be found in the psychology of perception. So-called ‘gestalt’ approaches examine not particular sensory stimuli, but the overall perception that one experiences in response to some complex visual scene or image. The more reductionist approaches of psychophysics, by contrast, attempt to isolate the precise responses to very specific stimuli (a single sound, a single point of light), etc, and observe how such atomic ‘sense data’ are combined to produce more complex perceptions. Another example can be drawn from the disciple of economics, where (very loosely) the subfield of microeconomics begins with individual decisions and attempts to derive properties of an economic system from the interaction of many individuals (a reductionist approach), whereas the subdiscipline of macroeconomics beings by analysing broad properties of the system as a whole without reference to specific individuals (a more holistic approach).
Many scholars would not consider it necessary to choose between reductionist and holistic approaches, but will use whatever methods they feel are most useful for their particular research interests. Nevertheless, certain philosophical and other ideas or viewpoints are typically more positively disposed to one approach over another. In particular, materialism and utilitarianism are often described as reductionistic ideologies, while dualism and virtue ethics are thought of as more holistic. Understanding this distinction is therefore of value when considering these questions.
Reductionism: brief introduction to the concept and comparison with opposing views from PhilosophyBasics.com
Reductionism: Internet Encyclopedia of Philosophy article discussing theories of an arguments over the concept of reductionism
Reductionism in biology: discussion of the application of reductionism to biology from the Stanford Encyclopedia of Philosophy
Reductionism and holism in psychology: discussion of the application of these ideas to psychological research and theory
Scientific reductionism: analysis of the strengths and weakenesses of reductionism in science