Halliday & Matthiessen (1999: 583-4):
A projection mental clause such as I (don't) think, since ideationally it realises a figure of sensing, construes the speaker as 'Senser at the time of speaking' (it occurs metaphorically only in simple present tense); at the same time, it enacts the speaker's own 'intrusion' into the dialogue — his or her judgment about how much validity can be attached to the proposition contained in the projected clause.
Interpersonal metaphor is thus the hinge between the ideational and the interpersonal modes of constructing the self. In the ideational mode we construe ourselves as conscious Sensers, while in the interpersonal mode we enact ourselves as speakers interacting with addressees; the metaphor brings the two together in such a way that the ideational construal stands for the interpersonal enactment (see Figure 14-6).
The grammar of everyday discourse thus clearly points to the significance of interpersonal meaning in the way that we construct ourselves — the self is not only construed but it is also enacted. Cognitive scientists, however, have derived their object of study, and their model of this object from the ideational perspective alone, failing to take the interpersonal perspective — that of enacting — into account.