  Throughout the literature, there are widely different motivations and standards of proof accepted, so that at times it can be hard to see any coherent body of work. Maxwell's original intention was to demonstrate that the second law had only limited validity, and that violations were possible. Although he originally described the demon as a living being, he later reduced its role to that of being a valve. Smoluchowski sought to tame the demon, by formulating a modified second law that it did not violate. His exorcism applied only to mechanical devices and he left open the question of whether intelligent intervention could reverse the second law. As the literature developed, both the scope of the exorcism and the nature of the demon changed. The concept of intelligence became reduced to that of information processing performed by a mechanical device. Rather than investigate how a tame demon might be constrained by physical laws the aim became to exclude demons altogether. Much of the resulting literature proceeds on a case-by-case basis, where individual examples of demons are argued to fail and it is simply extrapolated that all demons will fail for similar reasons.