Halliday & Matthiessen (2014: 703):
In the type of mood metaphor shown in Table 10-11, the proposition/proposal is realised by a clause nexus of projection rather than by a simple clause. The interpersonal projection embodied in speech function has thus been realised as if it was an ideational projection. This has two consequences for the expansions of the meaning potential of speech function, just as in the case of modality. On the one hand, the option of making the subjective orientation of the speech functional selection explicit is added to the system, as in vote against ... (implicit) vs. I urge you to vote against (explicit). On the other hand, the speech functional system can be further elaborated in delicacy by drawing on the extensive resources of the lexicogrammar of ‘verbal’ and ‘mental’ clauses. Thus in addition to vote against ..., we now have, for example, (‘verbal’) I tell you/command you/order you/ask you/urge you/implore you/ beseech you/plead with you/suggest to you → to vote against ...; (‘mental’) I want/desire/‘d like/ intend/plan → (for) you to vote against .... And while these clauses are constrained in terms of SUBJECT PERSON and DEICTICITY, they still allow for additional systemic variation; for example: I urge you/I would urge you/I should urge you/I must urge you//can I (please) urge you/could I perhaps urge you → to vote against ....