518. Though a complex sentence can have but one (simple or compound) main clause, there is, in theory, no limit to the number of subordinate clauses.

519. Subordinate clauses may be attached to the main clause (1) as separate modifiers or complements; (2) in a coördinate series of clauses, all in the same construction, and forming one compound clause; (3) in a series of successively subordinate clauses, forming one complex clause.

520. Two or more subordinate clauses may be attached to the main clause separately, each as a distinct modifier or complement.

521. Two or more subordinate clauses in the same construction, forming one compound clause, may be attached to the main clause as a modifier or complement.

In the first and second examples, three coördinate noun clauses are joined to make one compound clause, which is used as a complement,—as a predicate nominative in the first sentence, as the direct object of told in the second.

In the third example, a compound adjective clause modifies Ellis. In the fourth and fifth, a compound adverbial clause modifies the predicate verb (ordered, received). In the seventh, four that-clauses unite in one compound clause.

522. Two or more successively subordinate clauses, forming one complex clause, may be joined to the main clause as a modifier or complement.

In such a series, the first subordinate clause is attached directly to the main clause, the second is subordinate to the first, the third to the second, and so on in succession.