1 A sufficient condition of something else.
2 A condition that may not be sufficient for another, but can be seen a priori to provide good evidence for it. Thus the fact that someone is behaving appropriately may not guarantee logically that they arehe or she is in pain, but it may be a priori true that it is excellent evidence for it. The latter usage is attributed (controversially) to Wittgenstein. It fits with a generally holistic view of language, with assertions tied to each other by semantic forces of different strengths, rather than by straightforward logical relations.