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support the ally, and, knowing this, the ally will always concede to the challenger. Yet, the US
maintains a policy of strategic ambiguity and Taiwan’s decision to behave opportunistically is
nevertheless a function of what it believes the US is likely to do.
In our view, Zagare and Kilgour’s model has two key limitations. First, as George and
Smoke (1974) observed about traditional rational deterrence models, “Abstract deductivist
approaches to deterrence have tended to assume that commitments have a simple ‘either-or’
character. One is committed or one is not” (551). Strategic ambiguity is neither a full commitment
nor no commitment. Unlike traditional rational deterrence models, a model designed to capture
strategic ambiguity needs to include more than just a binary either-or option for the defender. An
ambiguity strategy includes a move in which the defender, instead of selecting a full or not
commitment, chooses not to reveal the level of its commitment. This move can be signaled
through a formally declared policy such as the US policy of strategic ambiguity. The inclusion of
an ambiguity move in a formal model will impact what subsequent moves are available to the
challenger and ally, and it will provide the leverage we need to determine the conditions under
which defenders will choose ambiguity over transparent alternatives.
Second, Zagare and Kilgour’s model assumes that the challenger is the only first-mover.
However, the crucial tension in the dual deterrence dilemma is the threat that either the challenger
or the ally can move first to destabilize the status quo. Having multiple potential first-movers
complicates deterrence strategies. If the defender agrees to a firm and transparent commitment,
then the blanket protection of the unequivocal defense guarantee creates an incentive for the
opportunistic ally to behave recklessly, likely creating a crisis and embroiling the defender in an
undesirable conflict. However, if the defender does not commit or if the defense commitment is
too low, then the challenger will be emboldened to initiate a confrontation believing that the
defender will not intervene. The defender’s dilemma is to determine how to strike a balance
between over-aggression and appeasement.
Convention