Before we move on to other punctuation rules, we want to point out that some sentences are both compound and complex. They’re called, not surprisingly, compound / complex sentences. You’ll see that in such a sentence a writer uses a coordinating conjunction and a subordinating conjunction. Here are two examples.

(a) Because Jesus Christ died on the cross, many Christians assume that the symbol originated with Christ’s death, but actually the cross had been used as a religious emblem for centuries before the crucifixion.

(b) This was the favorite saying of the great American actor Spencer Tracy: “You only live once, and if you work it right, once is enough.”