International Relations. A self-Study Guide to Theory

particles; however, Descartes did not believe in the indivisibility of these 
“corpuscles”. Corpuscle theory became an influential perspective at this time 
and remained so for many decades afterwards. For example, Thomas Hobbes 
drew on it when formulating his political theory in the Leviathan (1651) and 
Isaac Newton used it in his “corpuscular theory of light”, which will be dis-
cussed below.
In the Cartesian, mechanical, machine-like view of the world, it was as-
sumed that each corpuscle remains in a neutral state until it is given a “push” 
from the outside. After this initial contact, the corpuscle starts to move and 
continues to move constantly in a straight line until it collides again with an-

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other “corpuscle” (Bedenig 2011: 84). Descartes transferred this idea to the 
movement of celestial bodies. Its application to the solar system results in the 
conclusion that there must be a mechanism responsible for the earth moving 
around the sun: a “force” which compels the planets to move towards the sun 
and not “fly away” in straight lines (Bedenig 2011: 84). This “force” is in 
fact gravity, later discovered by Isaac Newton. The “mechanism” involved 
was mathematically formulated in Newton’s law of gravity.
Newton’s work thus “completed” the new mechanical world view. Isaac 
Newton is well-known as the father of classical mechanics and is hence a 
major contributor to what is known as classical physics. This term applies to 
physics until the end of the 19
th
 century; that is, before Einstein (for an over-
view see Bedenig 2001: 86-88). Newton formulated many of his major ideas 
in his Philosophiae naturalis principia mathematica (1687). Please note the 
term; physics at this time was considered to be a “natural philosophy”. 
In the year 1666, Newton made groundbreaking insights in a diverse range 
of fields: infinitesimal calculus (mathematics), optics and the theory of gravity. 
Of all his achievements, he is best-known for this last contribution, the discov-
ery of the gravitational pull as the physical law according to which each body 
in the universe exerts gravitational force towards other bodies. Newton’s laws 
of motion and of universal gravitation transformed astronomy (Bedenig 2001: 
87-88). Starting with Kepler’s Laws and continuing with Newton’s work, as-
trophysics developed as the “new astronomy”, merging physics and astronomy 
(with a basic understanding of physics as “natural philosophy”). 
As has been mentioned above, Newton’s work on the nature of light 
draws on corpuscle theory. Newton understood light as “corpuscle (particle) 
radiation”, the idea that light consists of tiny particles that are emitted from a 
light source in a linear manner. As you will learn in more detail in Step 2.4., 
this search for the nature of light belongs to the most important objectives in 
physics and cosmology.
From the introduction in Unit 2, you know that atomism is a specific posi-
tion on the philosophical problem of how particulars relate to the whole. You 
are also familiar with the argument that, in addition to ontological aspects of 
atomism, epistemological and methodological implications exist as well. 
These result in methodological individualism and reductionism. It will there-
fore be easy for you to see that the mechanical world view and corpuscle the-
ory are closely linked to methodology. For Descartes, to understand a system 
we have to divide the system into sub-systems. These sub-systems have to be 
analyzed separately, allowing the single effects of each sub-system to be ex-
amined more easily. Complex systems thus have to be “reduced” to simpler 
ones until causes of phenomena can be analyzed separately, undisturbed by 

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84 
interfering effects. Following this method, the direction of scientific thought 
should progress from the “simple” to the more complex (Bedenig 2001: 84-
85). This principle is referred to as reductionism or methodological individu-
alism, a major feature of positivist science with which you are already famil-
iar from your reading in Unit 2. Reductionism and methodological individu-
alism continue to be central positions in the sciences today. As we will see, 
they also play a crucial role in IR theory building.
Both Descartes and Newton have proven to be highly influential, as their 
concepts of atomism/reductionism/methodological individualism became 
widespread in European scientific thought. This prevalence is reflected in 
many ways, ranging from the general ontological assumption of an atomized 
material world to the specific types of explanation and methodology found in 
the sciences. For example, in the natural sciences atomism is prototypically 
embodied in classical, that is, particle physics (Harrison 2000: 2). In the so-
cial sciences, the perspective is prototypically reflected in (neo)classical eco-
nomics and liberal theory. Both these areas perceive the individual as a sepa-
rate entity, the basic unit of society and its institutions. In IR, the interpreta-
tion of the state building processes in Europe as progressing towards “units” 
(the sovereign states) and models of a states system comprised of these sepa-
rate entities (states) also embodies the fundamental atomist order of thought 
as developed by Newton and Descartes in European philosophy.
In short, since the 17
th
century, atomism/reductionism/individualism has 
come to shape the ontology, epistemology and methodology of the idea of sci-
ence to such an extent that it is now in fact taken for granted and remains to a 
great extent unquestioned. For a critical engagement with the atomism of Des-
cartes from a sociological perspective, see for example Norbert Elias 1987: