Adverbial clauses are subordinate clauses that modify their superordinate clauses. This modification can occur at various levels (such as verb phrase, tense phrase, mood phrase) and in various dimensions (such as times and worlds) and ways. These variations give rise to a categorization of adverbial clauses (temporal, modal, ...) and a subcategorization according to a range of relations within these dimensions, depending on the subjunction. Thus within the modal category it is customary to distinguish between causal, conditional, purpose, result, and concessive clauses. Sometimes the subjunction does not seem to encode much meaning of its own and the clause acts more like a relative clause, modifying a quantificational adverb or a modal, or specifying an underspecified predicate; sometimes, when there is no subjunction (“free” adjunct clauses), the contribution of the clause is underspecified.