Tutu uses addition (also, further) to add Arguments to support his Thesis. And he uses consequence (thus) to draw conclusions from each Argument. These items are not linking events in a field of experience beyond the text; rather they are used to link logical steps that are internal to the text itself. We refer to this system for logically organising discourse as internal conjunction. And the system for linking events in an activity sequence is known as external conjunction (after Halliday and Hasan 1976).
 To be clear, in terms of SFL theory, the wording 'field of experience' confuses the ideational dimension of culture (field) with the non-semiotic domain (experience) that is construed by the processes of consciousness as ideational meaning. This is an important epistemological distinction for a theory that takes meaning to be immanent (a property of semiotic systems only).
 This is misleading, because Martin & Rose are not following Halliday & Hasan (1976), since they demonstrably misunderstand the distinction between external and internal conjunction.
Firstly, both types of conjunctive relation are internal to the text. The external/internal distinction means external/internal to the communication situation. Halliday & Hasan (1976: 240):
Thirdly, the distinction between external and internal conjunctive relations is made on the basis of the metafunctional distinction between experiential and interpersonal, not experiential and textual. Halliday & Hasan (1976: 240):
 To be clear, in SFL theory, conjunction is a system of the textual metafunction on the stratum of lexicogrammar, which Martin (1992) has misunderstood and rebranded as his system of the logical metafunction on his stratum of discourse semantics.