  The sound horn proposes a resolution in which the demon, as well as the system, are assumed to be ‘canonical thermal systems' and so subject to, a possibly modified form of, the second law. By imposing some form of the second law, consideration of what information processing a demon may need to undertake would lead to a conclusion as to what the thermodynamic cost of that information processing must be. This approach lead Szilard to conclude that information acquisition had an intrinsic thermodynamic cost. It is possible to read some papers on the use of Landauer's principle in the Szilard engine in a similar way: the justification for believing that the resetting operation must carry a thermodynamic cost is for, otherwise, even a modified second law would be false.