Halliday & Matthiessen (1999: 550):
(2) Blendthey might win tomorrow— ability 'they may be able to'x— probability 'it is possible they will'Here, on the other hand, the meaning of the oblique modal might combines the two senses of 'able' and 'possible', rather than requiring the listener to choose between them. If the verbal group is 'past', however, this again becomes an ambiguity:they might have won— ability 'they were capable of winning (but they didn't)'— probability 'it is possible that they won (we don't know)'