International Relations. A self-Study Guide to Theory

made of particulars (ontology) but can be (methodologically) reduced to and 
explained by its elements. This has been described above as methodological 
individualism and logical atomism. For example, in logical positivism, theo-

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ries are reducible to elementary protocol statements; in materialist atomism, 
things are reducible to smallest indivisible particles etc. Both theories and 
material entities can finally be explained in terms of the particulars. 
The term reductionism might be seen as the broader, more general term. 
We are discussing it here in a separate paragraph because of its more funda-
mental nature as a specific mode of thought found at the heart of positivist 
science. The ontological as well as methodological and epistemological as-
sumptions of positivist science all reflect reductionism. However, when we 
say “reducible to”, we are usually referring to explanation and method.
The notion of emergence provides an example for the opposite of reduc-
tionism in explanation. Emergence describes a case in which a system or a 
thing possesses a property that is NOT reducible to the parts or single proper-
ties of its parts. It excludes the principle of reductionism. For example, in 
systems theory, hierarchically structured systems have properties on the mac-
ro-level that cannot be found on the micro-level. On the macro-level they oc-
cur, emerging from the interaction of their elements on the micro-level, but 
cannot be reduced to those elements or explained in terms of them. It requires 
a different methodology to reach an explanation of the system (the whole). 
This position has been referred to above as methodological holism. 
Reductionism in its broader meaning is also exemplified by the famous 
“Ockham’s razor”: the principle of parsimony/lex parsimoniae. It requires 
giving preference to the explanation based on the smallest number of hypoth-
eses and hence presents the most simple, parsimonious theory. The theory 
should include as few variables and hypotheses (standing in clear logical re-
lation to each other) as possible. In fact, the position of reductionism dates 
back to ancient Greece with Aristotle’s view that nature chooses the simplest 
way – which, incidentally, is an ontological claim. But with Ockham, parsi-
mony became an epistemological principle: the requirement that, when build-
ing theories, needless elements should be eliminated. Going further, in the 
case that different theories exist to explain the same phenomenon, Ockham’s 
position would give preference to the most parsimonious theory. This princi-
ple became influential in the 19
th
century and has been spread above all by 
John Stuart Mill. More recently, the principle has been called “economy of 
thought” (Denkökonomie, a term probably first used by Richard Avenarius). 
In short: In positivist science, the ontological claim of a material, atom-
ist/particularist/individualist world (that is, a world of observables) and an 
ontological nominalist position in regard to “universals” is complemented by 
an epistemological and methodological reductionism. For science this implies 
the following: in order to know about the “whole”, we have to study the parts 
which comprise it.

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57 
Unity of science 
Consequently, reductionism is also found in the positivist belief in the ideal 
of a unity of science. This belief holds that all phenomena of the world can, 
in the final analysis, be explained by the fundamental, elementary science: 
classical physics. This principle reduces all scientific disciplines to an “ele-
mentary science”, with the expectation of a unified perspective of reality. For 
example, a belief in the unity of science assumes that chemistry is reducible 
to physics (because a chemical element is reducible to the arrangement of at-
oms and molecules), that biology is reducible to chemistry (and chemistry 
then to physics), or psychology to biology or biochemistry (holding, for ex-
ample, that the explanation of depression is ultimately reducible to a lack of 
neurotransmitters, which in turn is “observable”/measurable).
In its most radical form, the belief in the “unity of science” ultimately re-
sults in the conclusion that even social sciences are reducible to physics or 
that a theory of the social sciences should be in line with the major findings 
of the natural sciences. The idea of the unity of science has been spread since 
the 1950s. Examples include Oppenheim and Putnam (1958). For a more re-
cent discussion as related to IR see Wendt (2006, 2010).
As an epistemological and methodological position, the assumption of a 
unity of science gives a privileged position to the natural sciences and their 
methodology. The idea emerges that any science, including the social scienc-
es, should be based on the methodology and model of explanation used in the 
natural sciences. Social science can therefore be studied in the same manner 
as natural sciences; there is a single scientific method which can analyze both 
the natural and the social world.
Contrasting arguments can be found in the works of Max Weber, Emile 
Durkheim, Wilhelm Dilthey, Martin Heidegger and Georg Gadamer, among 
others. These works claim that the social world requires a different form of 
analysis than the natural world, such as hermeneutics- the science of text in-
terpretation and understanding. They take this position because, in the social 
world, all analysis is embedded in language, history and notions of truth; rea-
son are themselves historically constituted. Further, in the social sciences, 
there can be no truly objective knowledge because the subject who interprets 
and observes is part of the world he/she is analyzing.
Reductionism can be seen as the most orthodox position both in the 20
th
century and today. It can be read as an absolutizing and prioritization of 
physics. The success of modern science unquestionably provides the back-
ground for the success of reductionism. However, a trend of antireductionism 
has been growing for about 30 years. This trend emerged mainly as a result 

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of findings in neurophilosophy or biophilosophy that demonstrate the prob-
lems of a reductionist explanation of phenomena such as human conscious-
ness. Phenomena of the social world or such as the human mind appear more 
generally not to be reducible to phenomena that can be explained by the clas-
sical approach of the natural sciences. In the social sciences, the spread of so-
cial constructivist theories, theorizing the existence of “immaterial factors” 
such as the role of norms, collective ideas and collective representations, and 
learning etc. also provides a good indicator for the growth of antireduction-
ism. In addition, the simple fact remains that a unifying of sciences did not 
take place in terms of methodology and epistemology. Rather, diversification 
occurred in terms of the ontological, epistemological and methodological po-
sitions that underlie theory building. For IR, this trend away from reduction-
ism became clear at the very latest in the so-called positivism-postpositivism 
debate, which has been taking place since the 1990s. This debate will be dis-
cussed in the next section (2.3.). 
Finally, let us conclude our discussion of positivism as an example for a 
philosophy of science by focusing on its notion of causality and the specific 
type of explanation. Reductionism goes hand in hand with a specific concep-
tion of causality and explanation: the idea that, ultimately, single causes ex-
ists for any phenomenon observed.
Causal, law-like explanation and the belief in prediction 
Positivism is based on the assumption that the material world of particulars is 
governed by laws and that we can gain scientific knowledge about this mate-
rial world and its laws through (positivist) science. The term “law” refers to 
regularities or the “order” of the world. With regard to explanation, positiv-
ism derives its understanding of the term explanation from a fundamental be-
lief in the existence of regularities or laws in the natural as well as social 
world. At the heart of these regularities are cause-effect-relationships be-
tween the entities.
In positivist science, explanations establish a causal relation, also called a