Joe Barnes, Bonner Means Baker Fellow at the James A. Baker III Institute for Public Policy, and Richard J. Stoll, PhD, Professor of Political Science at Rice University, wrote in a Mar. 2007 paper titled "Preemptive and Preventive War: A Preliminary Taxonomy":
"Preemption is the taking of military action against a target when there is incontrovertible evidence that the target is about to initiate a military attack. Prevention is the taking of military action against a target when it is believed that an attack by the target, while not imminent, is inevitable, and when delay in attacking would involve greater risk."
Karl P. Mueller, PhD, Senior Political Scientist at RAND Corporation, et. al, wrote in a 2006 report "Striking First: Preemptive and Preventive Attack in U.S. National Security Policy" on www.rand.org:
"Preemptive attacks are based on the belief that the adversary is about to attack, and that striking first will be better than allowing the enemy to do so. Preemption may be attractive because it promises to make the difference between victory and defeat, or merely because it will make the ensuing conflict less damaging than it would be if the enemy struck first. Preemptive attacks are quite rare, though the possibility of preemption was a central concern of nuclear strategists during the Cold War; the archetypical example is Israel’s attack against Egypt in 1967 that began the Six-Day War.
Preventive attacks are launched in response to less immediate threats. Preventive attack is motivated not by the desire to strike first rather than second, but by the desire to fight sooner rather than later. Usually this is because the balance of military capabilities is expected to shift in the enemy’s favor, due to differential rates of growth or armament, or the prospect that the opponent will acquire or develop a powerful new offensive or defensive capability. Israel’s 1981 raid on the Osirak nuclear facility was a classic preventive attack, as was Operation Iraqi Freedom, the U.S.-led invasion of Iraq in 2003.
Preemptive and preventive attacks have important differences; in addition to those already noted, international law holds that truly preemptive attacks are an acceptable use of force in self-defense, while preventive attacks usually are not. However, they are driven by similar logic, and since it is often useful to talk about both at the same time, the authors use the term anticipatory attack to refer to the broader category that includes both types of strategies. Anticipatory attack can be viewed as a continuum ranging from purely preemptive to purely preventive actions: All of them are offensive strategies carried out for defensive reasons, based on the belief that otherwise an enemy attack is (or may be) inevitable, and it would be better to fight on one’s own terms. Preemptive and preventive attacks are distinct from 'operational preemption,' taking military actions within an ongoing conflict that are intended to reduce the enemy’s capabilities or to achieve other effects by acting before the enemy launches an attack or takes some other undesirable action, such as deploying or dispersing its forces. Anticipatory attacks often involve operational preemption, but need not do so, and operational preemption may occur in any sort of conflict."
James J. Wirtz, PhD, Professor of National Security Affairs at the Naval Postgraduate School, and James A. Russell, MA, Senior Lecturer in National Security Affairs at the Naval Postgraduate School, wrote in a Spring 2003 Nonproliferation Review essay "U.S. Policy on Preventive War and Preemption":
"Although the terms often are used interchangeably, 'preventive war' and 'preemption' are distinct strategic concepts. Preventive war is based on the concept that war is inevitable, and that it is better to fight now while the costs are low rather than later when the costs are high. It is a deliberate decision to begin a war. Preventive war thinking seems to dominate Bush administration planning about Iraq: It is better to destroy Saddam Hussein's regime now than to deal later with a regime armed with nuclear weapons or other WMD. Preventive war thinking, however, can turn out to be a self-fulfilling prophecy, since treating war as inevitable can help make it inevitable. It also can lead to unnecessary conflict because few things are inevitable: Saddam could die of natural causes next week, producing a significant opportunity for the United States and its allies to shape Iraqi politics and policies.
Preemption, by contrast, is nothing more than a quick draw. Upon detecting evidence that an opponent is about to attack, one beats the opponent to the punch and attacks first to blunt the impending strike."
The Council on Foreign Relations' Boston Term Member group, in a Feb. 1, 2004 summary paper titled "The Bush Administration's Doctrine of Preemption (and Prevention): When, How, Where?" wrote:
"The difference between preemptive war and preventive war is not a matter of semantics. Rather, it is a matter of timing that has implications for whether an act is justified or not. Traditionally, preemption constitutes a 'war of necessity' based on credible evidence of imminent attack against which action is justified under international law as enshrined in the self-defense clause (Article 51) of the UN Charter. But the Bush administration has expanded the definition to include actions that more closely resemble preventive war. Preventive wars are essentially 'wars of choice' that derive mostly from a calculus of power, rather than the precedent of international law, conventions and practices. In choosing preventive wars, policymakers project that waging a war, even if unprovoked, against a rising adversary sooner is preferable to an inevitable war later when the balance of power no longer rests in their favor. The proposition gains traction when that enemy state is arming itself with WMD, or credibly threatens the supply of a critical resource such as oil, and national intelligence indicates that the enemy intends to harm one's own state."