A negative conditional relation is a conditional relation
Unless it rains, we’ll have our picnic.
I was not informed; otherwise I should have taken some action.
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 . 1977.Text and context: Explorations in the semantics and pragmatics of discourse. London: Longman.