Halliday & Matthiessen (2014: 271-2):
Like other processes, processes of attribution unfold through time. In the unmarked case, the phase of the unfolding is left unspecified (‘neutral’); alternatively, the phase is marked as either (1) ‘time phase’ – ‘inceptive’ (e.g. become, go, grow, turn) or ‘durative’ (e.g. keep, remain) or (2) ‘reality phase’ – ‘apparent’ (e.g. seem, appear), ‘perceptive’ (e.g. look, sound, taste) or realised (e.g. prove, turn out)…