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Dugald, These are only recommendations, presumably so those who choose to use them can be understood by all. Thus, using paper three's recommended nomenclature, I can clearly write 'An upward flux of dense CO2 might metamorphose an amphibolite into a granulite. During this prograde metamorphism the metamorphic grade did not change, though an isograd did move across the rock. The facies, too, did not change. Its name, however, did.' Of course, you might choose not to use the SCMR nomenclature, because it would make your elegant study of intersecting isograds an amusing read. Unless petrologists are happy with this new clarity, the SCMR committee would be happy to hear from you. They have been requesting criticism for four years. One might also carefully consider Prof Banno's suggestion of public discussion. If the SCMR members are voting on individual definitions, this might explain the lack of fit of related definitions. Personal opinions Within the theory of thermodynamics, variables such as temperature & pressure are artificial: artifacts of the design of laboratory experiments. Perhaps natural definitions should not use these. Those papers I have read have used 'grade' fundamentally as a relative measure of the intensity of metamorphism, using an ordered scale of isograds. Isograds were curves on the surface that separated (zones of) metamorphism of higher & lower intensity. Each was prefixed by that observable criterion the geologist used to make this determination. After much mapping of this nature, geologists used terms such as 'low grade' to characterize the intensity of metamorphism in a region as being lower than usually observed. Respectfully, Bruce Bathurst