  This kind of eliminative argument has significant weaknesses. All possible sources of entropy increase are eliminated and it is concluded whatever is left must be responsible for any remaining entropy increase. It is hard to see how it can be considered an explanation of why demons do not exist, as by imposing the second law in the first place, one has simply ruled out their possible existence. At most it can provide a demonstration of the consistency of assuming some particular operation has a thermodynamic cost attached to it. It is also hard to see what confidence one can have in the conclusions of such an argument. Szilard, Gabor and Brillouin thought that such arguments led to the conclusion that information acquisition had an intrinsic cost. By contrast, Landauer, Penrose and Bennett concluded that information acquisition does not have an intrinsic cost, but information erasure does. What are the grounds for supposing Landauer's principle is any more secure than Szilard's argument?