Well, following Yongdzin Rinpoche, JLA insists a lot on that distinction. In Bön texts, Rigpa and Marigpa are considered as "modes" (tshul) in which Mind (sems-nyid) or mind (sems) function in their respective manner. In other words, the ordinary mind (sems) functions in a mode which is that of Marigpa/ignorance (no recognition of the epiphany of the Base) while Mind itself (sems nyid) is functioning in the mode of RIgpa/knowledge (recogntion of the nature of the epiphany of the Base). In this second mode (that of Rigpa), the Mind "discerns" (rig) its own nature by spontaneously understanding and experiencing the separation of the pure from the impure (dwangs snyings phyed), pure being a generic code term for anything unconditioned or nirvanic and impure another code term for anything conditioned or samsaric.heart wrote: I certainly never heard him do that distinction, nor have I ever heard anyone else do it except for you Malcolm.
Thus in the same way our ordinary mind works in a mode of ignorance right now without the faculty to discern (rig) its own nature, our Mind (sems-nyid) discerns (rig) its own nature and, in ZZNG wording, is the Absolute Body (bon-sku) knowing itself (rang-rig) and having no (other) "object" (of course it's not an object in a literal sense even though in Bon Dzogchen logic texts, this could be explained as such). But you'll get some texts which, out of poetic license, don't make difference between Mind (sems-nyid) and Rigpa (The Twenty-One Seals for instance), but in the end this is not a mistake, it's a literary shortcut. Of course, it may create confusion but Rigpa has been nearly reified in the mind of westerners so I guess it's important to understand the subtleties of identifications (for the sake of simplification) or distinctions (for the sake of clarification), both actually leading to understanding.
However, as far as translation is concerned, I don't know why but in English Mind (sems-nyid) is often (always?) rendered by "nature of the mind". This is actually a definition not a translation. Sems-nyid is "Mind itself" or "Mind" if you want to drop the "itself". Choosing Mind or Mind itself would help avoiding ridiculous renderings when encountering sentences like "sems-nyid sems kyi rang bzhin yin/" -- "The nature of the mind (sems-nyid) is the nature of the mind (sems kyi rang bzhin)", which I guess all here would consider as silly, no?