Halliday & Matthiessen (1999: 378):
The text base is oriented towards the ideation base and the interaction base. It provides the resources for constructing meanings from these two bases as information of a kind that can be shared as text. An ideational figure and an interpersonal move are constructed as information in the form of a message. Such a message is related to the preceding discourse and differentiates informational statuses in terms of thematicity and newsworthiness. From the speaker's point of view, the text base is a resource for developing a text, message by message, and for guiding the listener in his/her interpretation of the text; and from the listener's point of view, it is a resource for constructing such an interpretation.