To write a compound sentence, join two or more independent clauses together into one sentence. When using two independent clauses, separate them by placing a semicolon between them or by putting a semicolon after the first one followed by a conjunctive adverb and then a comma. Alternatively, separate the two by putting a comma after the first independent clause followed by a coordinating conjunction.
An independent clause is a group of words that contain both a subject and a predicate and can stand alone as a sentence. Coordinating conjunctions are short conjunctions such as "and," "or" and "but." Conjunctive adverbs are words such as "therefore," "however," "moreover" and "consequently." The choice of the conjunctive adverb or the coordinating conjunction tells something about the relationship between the two independent clauses.
An example of the first way to make a compound sentence is "The boy put ice in the glasses; his sister poured the tea." This sentence has two separate complete thoughts joined by a semicolon. The second independent clause is not capitalized.
In the sentence "The boy put the ice in the glasses; however, his sister poured the tea," the two clauses are joined by a conjunctive adverb. A semicolon precedes the adverb, and a comma follows it.
In the example, "The boy put the ice in the glasses, but his sister poured the tea," the clauses are separated by a comma and a coordinating conjunction. If three or more independent clauses make up the compound sentence, the conjunction typically comes before the last one.