Halliday & Matthiessen (2014: 368):
Non-specific Deictics are given in Table 6-3; they are total or partial determiners. The total ones convey the sense of ‘all’ (positive) or ‘none’ (negative), and the partial ones convey the sense of some unspecified subset; for example, both trains have left, is there a train leaving soon?, there are some trains on the track, some trains are very comfortable, I haven’t noticed any trains go by.
