[...] the interpersonal [component], is language as the mediator of role, including all that may be understood by the expression of our own personalities and personal feelings on the one hand, and forms of interaction and social interplay with other participants in the communication situation on the other hand.
- Halliday (1973), a pag.66

The interpersonal component is the grammar of personal participation; it expresses the speaker’s role in the speech situation, his personal commitment and his interaction with others.
- Halliday (1973), a pag.99