Magruder’s Principle

1-42. Magruder’s principle states that it is generally easier to induce the deception target to maintain a preexisting belief than to deceive the deception target for the purpose of changing that belief. Magruder’s principle exploits target biases and the human tendency to confirm exiting beliefs. Magruder’s principle alludes to two paths. A path of the deceiver changing the belief of a target and a path of maintaining a present belief. The principle then advises the better of the two paths. Magruder’s principle is named for Major General John Magruder. During the Civil War, he was tasked with impeding Major General George McClellan’s advance on Richmond with a numerically superior force. Magruder deceived McClellan by encouraging McClellan’s belief that he faced a larger enemy than he actually faced. In using Magruder’s principle, MDOs provide the targeted decision makers with information that reinforces their expectations for what they believe to be true. This reinforces the target’s pre-existing perceptions. Any bias is potentially exploitable. Most targets are unaware of how deeply their biases influence their perceptions and decisions. Most people resist letting go of existing opinions and tend to seek information that reinforces their own bias.

1-43. An example of this principle occurred with the selection of the invasion site and its cover plan for the D-Day invasion of France. Using reconnaissance and communications intercepts, the Allies learned that Hitler and his senior military advisors believed that the most likely place for the Allied invasion would be in the Pas de Calais region. This was a viable plan as it provided better air cover and a shorter transit time from England; in fact, it was a reverse of their plan to invade England in 1940. The Allies were able to exploit and reinforce the enemy’s expectations to the extent that the Germans had a difficult time reacting to the actual landings in Normandy.