Matthew Kroenig’s provocative piece for Foreign Policy claimed that “realism has become unrealistic” but his entire argument rests on a flawed conceptual foundation: he treats Realism as though it were a monolithic theory with a single set of predictions. It is not. Realism is better understood as a paradigm, a school of thought or a family of theories. In addition to classical realism, it encompasses multiple distinct approaches, including neorealism with its defensive and offensive variants, and neoclassical realism. These theories share important assumptions about power, security, competition, and the constraints imposed by international anarchy, but they differ substantially in what they seek to explain, how they conceptualize causation, and what they predict about state behavior. This distinction matters because Kroenig’s central criticism that Realism has repeatedly failed to explain the U.S. foreign policy behavior depends on aggregating the predictions of different realist theories and treating their explanatory power as a failure of Realism as a whole. However, that is not a satisfactory way to evaluate the validity of a paradigm.

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Kroenig is right about one thing: theories should be confronted with empirical evidence. If a theory repeatedly generates predictions that are contradicted by observable behavior, scholars should reconsider its assumptions. But the appropriate unit of evaluation is the theory or model that actually generates the prediction. One cannot discredit an entire paradigm simply by demonstrating that particular theories within that paradigm have made particular predictions that turned out to be wrong.

Consider neorealism. Kenneth Waltz’s structural realism emphasizes the international system, particularly the distribution of capabilities among states, as the principal determinant of international outcomes. It deliberately abstracts away from many domestic-level variables and stipulates that it is not a theory of foreign policy but rather a theory of international politics that primarily concerns itself with explaining how systemic balances of power form recurrently.

Offensive realism, associated most prominently with John Mearsheimer, makes a stronger and different claim: because states exist in an anarchic system and cannot be certain about one another’s intentions, great powers have powerful incentives to maximize their relative power and ultimately seek regional hegemony. Defensive realism reaches different conclusions. Scholars such as Charles Glaser, Jeffrey Taliaferro, and Stephen Walt have emphasized that security does not necessarily require unlimited accumulation of power. Excessive expansion can provoke balancing coalitions and thereby make states less secure. From this perspective, the optimal strategy for a state depends on the security environment, the offense-defense balance, the intentions and capabilities of other states, and the costs of expansion. These are not semantic variations on one theory. While inhabiting the big tent of Realism, they are competing theoretical propositions that result in a distinctly diverse set of predictions about world politics in general and particular states altogether.

And then there is neoclassical realism, which is particularly important for understanding U.S. foreign policy nowadays, according to Kroenig’s key yardstick. Neoclassical realists accept the importance of systemic pressures but argue that the international distribution of power does not translate automatically into foreign policy behavior. The effects of systemic incentives are mediated through domestic political institutions, leaders’ perceptions,........

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