Punctuation Point: Joining Independent Clauses

Recently, someone asked me about joining two independent clauses to make a compound sentence. She thought such a sentence would need a comma, but she often found them missing. Today, we'll review how to join independent clauses.

First, a couple of definitions. A clause is a part of a sentence that contains a subject and a verb; it may or may not contain other words. An independent clause can stand as a sentence on its own because it contains a complete thought:

I ran.

Alternatively, a dependent clause does not contain a complete thought and can't stand on its own:

Although I was hungry

A compound sentence is two or more independent clauses (sentences) joined together:

President Obama and Korean President Lee failed to reach agreement on the Korean Free Trade Agreement (FTA) before a joint press conference in Seoul Thursday, but both leaders said the two sides will continue to work towards a final consensus in the near future.

What punctuation do you use between two independent clauses? You have a few options, depending on what parts of speech you use to join the sentences.

• Coordinating conjunctions. If you use one of the coordinating conjunctions–and, but, for, nor, or, so, or yet–to join two independent clauses, use a comma before the conjunction:
  

  Swift action saves a man's life, but paramedics fear electric-shock victim may have suffered internal burns to organs.

• Adverbs. If you use an adverb, such as however, nevertheless, or thus, use a semicolon before the adverb and a comma after:
  

  We expect average subscription prices to stay around current levels in the near term; however, if promotional activities continue longer than expected or new content agreements adversely impact Dish, this could lower our price estimate of $25.84.

  Note, however, that if you use therefore or thus and you don't need to emphasize the following clause, you can drop the comma:

  The plane took off late due to poor weather conditions; thus we arrived late.

• Transition expression. If you use a phrase such as for example, similarly, or namely, use a semicolon before the adverb and a comma after:
  

  After 45 days of no rain, the farmers were worried about their crops; indeed, it was all they thought about.

• Just punctuation. You might choose to join your independent clauses with just punctuation; in that case, use a semicolon (as this sentence does), a colon, or an em-dash.

In The Copyeditor's Handbook, Amy Einsohn succinctly lays out the rules (IND stands for independent clause):

IND, coordinate conjunction IND.
IND; adverb [,] IND.
IND; transitional expression, IND.
IND; IND. or IND: IND. or IND–IND.

For a deeper explanation and more examples, check out pages 78-79 of Einsohn's book.

Do you have more questions on joining clauses? Leave a comment below!