Explanation

A compound sentence is composed of two simple sentences joined by a semicolon or a comma with a coordinating conjunction, showing a clear connection between equal ideas.

Imagine the relationship between simple sentences within a compound sentence as items on either side of a balance scale. Each sentence retains its completeness, but by physically connecting them, the writer encourages the reader to recognize a relationship between the ideas each expresses.

Construction Options

Semicolon

The semicolon acts as a sturdy bolt for joining sentences. A writer would choose this connection if the two sentences to be joined are so clearly related that the reader will automatically understand the connection.

Pirates drink rum; it helps them get their sea legs.
(subjects are bolded and verbs italicized throughout this page)

Pirates are expert sailors; they swarm up the rigging and unfurl the sails.

Comma and Coordinating Conjunction

A writer will choose the comma and coordinating conjunction to indicate how the ideas are related. Each coordinating conjunction does a different job. And asks the reader to join the two ideas. So indicates a cause/effect relationship, etc.

The island was dangerous, so the pirates moved in.
(The pirates chose the island because of its dangerous nature.)

The island was dangerous, yet the pirates moved in.
(The pirates moved in despite the dangerous nature of the island.)

The island was dangerous, for the pirates had moved in.
(The dangerous nature of the island is a result of the pirate occupation.)

A mnemonic device (memory trick) for remembering the coordinating conjunctions is the acronym FANBOYS:

For
And
Nor
But
Or
Yet
So

CONJUNCTIVE ADVERBS

This third way of legally joining two complete sentences, just like the comma with coordinating conjunction, gives the reader a stronger sense of how the two ideas are related.

The correct punctuation for these connectors is: sentence; conjunctive adverb, sentence.

In essence, these two sentences are being joined by the semicolon with the conjunctive adverb acting as a transition from the first idea into the second.

The Pirate Queen was suspicious of the clever thief; as a result, she buried the gold coins.

The Pirate Queen was ruthless; however, she had a soft spot for clever thieves.

The clever thief was supposed to walk the plank; instead, he escaped with the gold.

Common Conjunctive Adverbs

* “Conjunctive Adverbs.” Wikipedia. Wikimedia Corp. 21 Oct. 2013. Web. 23 Oct. 2013.