Halliday & Matthiessen (1999: 478):
To the extent that intentionality enters into the semantic system of a language, it could in principle be construed ideationally as some aspect of the overall system of figures or be enacted interpersonally as a modality of inclination. If it is construed ideationally, it could in principle be a global property of a figure as a whole or a local property of the process or a participant.In English, intentionality can be enacted within the interpersonal system of imperative modality (modulation) in the form of inclination, as in he won't be ordered around ('refuses to be'). It is independent of ideational agency; inclination is oriented towards the Subject, i.e. the modally responsible element of the clause, rather than (say) the Actor or Agent (as our passive example illustrates).Intentionality can be construed in the clause as circumstances of Manner ('according to plan', e.g. he found the book by chance; he turned left by mistake; he turned left intentionally) and as verbal group complexes of projection or enhancement realising the Process (e.g., she intended to leave at 4; she happened to be in the neighbourhood). It may also be a factor in certain lexical contrasts within delicate process types; but we have no evidence that intentionality is a primary variable in the semantic system of figures and its grammatical construal in transitivity. Rather, whether an example is read as construing something as intentional or non-intentional will depend on a variety of factors, such as the consciousness of the most active participant.