An additive relation is an interpropositional relation in which the propositions are judged either to be closely related or built one on another.
(English)
Halliday and Hasan believe that the words further, moreover, and also additionally indicate emphasis.
Thompson, Sandra A., and Robert E. Longacre. 1985. "Adverbial clauses." In Shopen 1985c
Halliday, M. A. K., and Ruqaiya Hasan. 1976.Cohesion in English. London: Longman.
Dijk, Teun van. 1981.Studies in the pragmatics of discourse. The Hague: Mouton.