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A simple sentence contains a single clause. If a sentence contains at least two independent clauses, it is called a compound sentence. The clauses in compound sentences are joined by a coordinating conjunction (and, but, or, for, so). The independent clauses could stand alone as sentences, but joining them implies a relationship between them.
- I studied for days, but I barely passed the test.
- Last summer was hot and dry, and the risk of wildfires was severe.
If a sentence contains one independent clause and one dependent clause, it is called a complex sentence.
- I remember the lessons that you taught me.
- The shirt was ruined because I spilled grape juice on it.
If a sentence contains at least two independent clauses plus at least one dependent clause, it is called a compound-complex sentence.
- Although the forecast predicted rain, the fair was held as planned, and attendance was good.
Punctuating Clauses within Sentences
If two independent clauses are joined by a coordinating conjunction, use a comma before the coordinating conjunction.
- The surgery was successful, and the patient recovered fully.
- The road is blocked, so we must take an alternate route.
Two independent clauses can also be joined without a coordinating conjunction; use a semicolon to separate the clauses. (The semicolon can also be followed by a conjunctive adverb and a comma.)
- The surgery was successful; the patient recovered fully. (semicolon only)
- The road is blocked; therefore, we must take an alternate route. (conjunctive adverb)
If an independent clause is followed by a subordinate clause, usually no punctuation is required at the join. But if the subordinate clause comes before the independent clause, use a comma at the end of the subordinate clause.
- I went to work even though I was feeling ill. (no punctuation needed)
- Even though I was feeling ill, I went to work. (subordinate clause comes first; follow with a comma)