Perfect deterrence theory and classical deterrence theory are two theoretical frameworks that have divergent empirical implications and dissimilar policy recommendations. In perfect deterrence theory, threat credibility plays a central role in the operation of both direct and extended deterrence relationships. But credible threats are neither necessary nor sufficient for deterrence to prevail, and under certain conditions, the presence of a credible threat may actually undermine deterrence. In perfect deterrence theory, the cost of conflict and status quo evaluations are also important strategic variables. Classical deterrence theorists tend to fixate on the former and ignore the latter. This theoretical oversight precludes a nuanced understanding of the dynamics of deterrence.