Halliday & Matthiessen (2014: 484):
With a finite clause, the conjunction serves to express both the dependency (the hypotactic status) and the enhancing relationship. As well as simple conjunctions such as because, when, if, and conjunction groups like as if, even if, soon after, so that, there are three kinds of complex conjunction, one derived from verbs, one from nouns and the third from adverbs.