There are restrictions on the combination of an adverbial clause with a main clause. It may or may not be possible to combine them, depending on their semantic and pragmatic nature. The relationships between an adverbial clause and a main clause can be divided into five types, which are termed the 'five levels in clause linkage'. On the basis of the research on the five levels in clause linkage in Japanese, the present collaborative research project investigates the combinatory possibilities of adverbial clauses --- mainly causal, conditional, and adversative clauses --- and main clauses in close to 30 languages of the world.