A compound sentence has at least two independent clauses.
People makes me grouchy, and I have been trying for months to figure out why.
— Nora Ephron, "People Magazine"
The independent clauses express ideas of equal importance and may be combined in one of three ways. They may be joined by a comma and a coordinating conjunction.
Some people start college right after high school, but they can't afford to finish in four years.
The two clauses may be separated by a semicolon.
Some students pay for college tuition by working; others are able to secure a scholarship.
Finally, the two clauses may be joined by a semicolon, followed by a conjunctive adverb, followed by a comma.
Many students go to school and work part-time; however, they rarely finish college in four years.
Independent clauses of similar length and construction make the compound sentence a balanced sentence.
I spent my summer vacation in Switzerland , and I traveled to Aruba during the winter break.
Change a compound sentence to a complex sentence or a compound-complex sentence if the ideas in the clauses are not all of equal importance. (See also subordination.)
change I saw the northern lights, and I have always been awed by them, so I stood still and gazed at them, [compound sentence]
to Seeing the northern lights, which have always awed me, I stood still and gazed at them, [complex sentence]
