Chapter 9-2-2: The Compound Sentence
A compound sentence consists of two or more independent clauses (or simple sentences) joined by a semicolon (“;”) by co-ordinating conjunctions like "and," "but," and "or" that are preceded by a comma, or with an adverbial conjunction that is preceded by a semicolon and followed by a comma:
Constructing Compound Sentences
Compound sentences are very natural for English speakers -- small children learn to use them early on to connect their ideas and to avoid pausing (and allowing an adult to interrupt):
Of course, this is an extreme example, but if you over-use compound sentences in written work, your writing might seem immature.
A compound sentence is most effective when you use it to create a sense of balance or contrast between two (or more) equally-important pieces of information.
Comma splices and run-on sentences (also known as fused sentences) are all names given to compound sentences that are not punctuated correctly. The best way to avoid such errors is to either:
punctuate compound sentences correctly by using one or the other of the rules further below; or
avoid compound sentences and write short sentences that require little or no internal punctuation.
Examples of Incorrect Sentences
If you're curious to see examples of run-on sentences, comma splices, and fused sentences, expand this item.
A run-on or fused sentence happens when writers join two complete sentences without any punctuation mark at all:
A comma splice happens when writers use a comma to join two complete sentences without placing an appropriate connecting word between them or by creating two separate sentences. Grammarians say that the comma just isn't "strong enough" to do the job of making one grammatical sentence out of two sentences in a scenario such as this:
How to Create Compound Sentences
There are three ways to create a compound sentence. The form of these sentences is:
① Independent clause; independent clause.
② Independent clause, coordinating conjunction + independent clause.
③ Independent clause; conjunctive adverb, independent clause.
Here is an explanation for each of these situations:
① The first case involves punctuation. It is possible to join two originally-separate sentences (independent clauses) into a compound sentence using a semicolon.
New York has better clubs; Montréal has better restaurants.
② Second, people can link two simple sentences together using a coordinating conjunction (for, and, nor, but, or, yet, so). The conjunction is preceded by a comma.
Montréal has better restaurants, but Toronto has better cinemas.
③ Finally, a conjunctive adverb (furthermore, moreover, however, nevertheless, indeed, in fact, consequently, therefore, otherwise, meanwhile) that is preceded by a semicolon and followed by a comma can be used.
Toronto has better cinemas; however, New York has better clubs.