Compound-complex sentence

A compound-complex sentence contains at least two independent clauses and at least one dependent clause, so it both ranks one idea above another and sets two ranked ideas side by side.

Although the key was bent, the lock turned, and the door swung in on an empty hall.

Count them: one dependent clause (although the key was bent), then two independent clauses joined by and. That combination is what the name describes — it is the fourth and largest of the basic sentence forms, after simple, compound and complex.

The form exists because some moments genuinely have that shape: a condition, a result, and a consequence, all belonging to one breath. Broken into three sentences, the sequence would read as three separate events rather than one continuous one.

The risk is proportional to the length. A compound-complex sentence asks the reader to hold a subordinate idea while two main ideas resolve, and if the clauses are long, or if the dependent clause is parked in the middle, the reader loses the thread and has to restart. Two safeguards: keep the dependent clause at one end rather than buried, and make sure the two independent clauses are genuinely equal — if one is an afterthought, it belongs in a dependent clause too.

For a long sentence that grows by adding detail rather than by stacking clauses, see the cumulative sentence, which is easier to read at the same length.