Realism and World Politics

structural theory, Theory of International Politics(1979), contains a comparative
discussion of ‘political institutions’ (also called ‘governmental systems’) in Britain
and the United States that could have been have been taken directly fromForeign
Policy and Democratic Politics.^20 Preceding this discussion, however, is a newly
developed conceptualization of structure.

A domestic political structure is thus defined, first, according to the principle

by which it is ordered; second, by specification of the functions of formally

differentiated units; and third, by the distribution of capabilities across those

units... The three-part definition of structure includes only what is needed

to show how the units are positioned or arranged. Everything else is omitted.^21

Thanks to a readily identified ordering principle, ‘Structure is not a collection of
political institutions but rather the arrangement of them’. For the political structure
of the state, this principle is hierarchy. ‘The units – institutions and agencies – stand
vis-à-vis each other in relations of super- and subordination’. Thus organized,
‘governmental institutions and offices’ engage in functionally specified activities as
the ‘concrete counterparts’ of functionally differentiated structures.^22
By contrast, international politics constitute a system consisting of functionally
undifferentiated units, or states, over which there is no political structure or, con-
cretely, subordinating institutions. Anarchy is the organizing principle, not
hierarchy.^23 In ‘Theory of International Relations’ (the version of Waltz’s structural
theory appearing in 1975), he was more concise. ‘Domestic systems are centralized
and hierarchic. International systems are decentralized and anarchic’.^24

Models, theories, science

In his 1967 essay, Waltz made passing reference to the balance of power as a model.
In the 1970s, he specified his conception of modelto anchor his definition of theory
and illustrate a theory’s relation to reality. Although Waltz’s views on theory are well
known, I want to emphasize – as few other scholars have – the importance Waltz
attached to models in linking theories to ‘the real world’.^25

A theory, while related to the world about which explanations are wanted,

always remains distinct from that world. Theories are not descriptions of the

real world; they are instruments that we design in order to apprehend some

part of it. ‘Reality’ will therefore be congruent neither with a theory nor with

a model that may represent it.^26

The referent for the pronoun ‘it’ concluding this passage is not reality but theory.
Waltz held that the term modelhas two senses: ‘a model represents a theory’ or ‘a
model pictures reality while simplifying it, say, through omission or reduction in
scale’.^27 Precisely what Waltz meant by the term representin this context is not at all
clear. I suggest that every theory is, or must take the form of, a model, that theories

92 Structure? What structure?