:::Thank you for your response. As you say, the article needed to make it clear that the "entropy of mixing" can refer to two factors, volume availability and molecular difference. I think that Fowler and Guggenheim (1939/1965 reprint, on pages 163-164) were right to focus on which are the independent variables. Careful statement should be able to get round this muddle. I think time spent by the writer, carefully stating which are the independent variables, and other formalities, are many times saved for the reader. I do not think we should let the usages of ordinary language completely over-rule the need for consistency and clarity in thermodynamics. Following Fowler and Guggenheim, I have tried to define it in the lead by referring to definite volume. I propose that the changed reference-volume factor is a recognized muddle and we should not nourish it. For thermodynamics, the changed reference-volume factor is a matter of diffusion, not a true mixing effect, I say. The molecular difference effect of interest to you is the true mixing effect, I say, and this should be signalled by including the fixed volume statement in the definition as proposed in effect, by Fowler and Guggenheim. So I say, let's put " " marks around the changed-volume version. Macroscopically, for gases, one could define mixing at fixed volume by requiring both components each separately to have the final mixed volume in the initial state, and the process to proceed by compressing them and then slowly removing the partition between them so as to let them expand slowly again into the common final volume. I suppose this would work for suitable gases, though hardly for liquids, which are the commoner materials of interest. But for all cases I think careful definition as suggested by Fowler and Guggenheim should be used to cut out the unnecessary muddle, rather than our sustaining the muddle just to comply with an over-the-top "ordinary language over-rules all" approach. The "Gibbs' paradox" story is verging on a waste of time and effort, and should be minimized. Gibbs himself did not see a paradox. In the article as it stands I see hardly any explicit statement that one is thinking in terms of controlled volume or controlled pressure or whatever. The article, as it stands, jumps straight from an apparent macroscopic thermodynamic approach into a statistical mechanical approach, without a blink. I am inclined to think that, in some respects, the statistical mechanical version actually increases confusion about Gibbs' paradox rather than dispelling it. Quite likely it will be possible to partly re-write and improve the whole article to make more sense of the physics.