"If I were compelled to define doctrine in a single sentence, that sentence would be: “Doctrine is a tangible representation of a military’s institutional belief system regarding how that military understands, prepares for and (in theory at least) conducts military activities.” To this general definition, which is derived from that contained in an earlier and more comprehensive study, some caveats must be added.
First, doctrine differs from theory because it is institutional. Even if a significant minority of the institution’s members disagree with doctrine, it nevertheless remains a representation of a military’s institutional beliefs. The official endorsement and institutional attribution of doctrine manuals symbolize this. Second, contemporary doctrine takes the form of written manuals. This was not always the case (see below), however when most people think of doctrine today, they think of written tomes. This is because written doctrine has become commonplace in Western militaries, and is the most visible type of doctrine. Finally, doctrine is cognitive in nature, since it is both part of and the result of a process of knowledge acquisition, assessment and distribution. Doctrine is inherently subjective because its content reflects a belief system. By making this system, or at least parts of it, tangible, doctrine is by necessity simplified and can only ever present an incomplete representation of strategic, operational and tactical realities."