Once you can identify a basic sentence, you can join or separate your sentences to best communicate your ideas.
A compound sentence joins two or more sentences that have related ideas of equal importance. The two sentences go together. Each sentence or independent clause must still have a subject and a verb.
For example:
She wanted spinach salad; he wanted a hamburger.
He went to the party, but she stayed home.
One way to create a compound sentence is with a semi-colon.
Not a common practice, a semi-colon is used only where ideas are very closely related.
For example:
She loves me; she loves me not.
They say it's your birthday; it's my birthday too! - Paul McCartney
Management is doing things right; leadership is doing the right things. - Peter Drucker
Another way to create a compound sentence is with a coordinating conjunction.
Coordinating conjunctions are sometimes referred to as FANBOYS. Notice how a comma is used with a coordinating conjunction.
For – He couldn't go home, for he had no place to go.
And – I took a taxi, and she drove home.
Nor – He didn't want help, nor did she offer it.
But – I wanted to go late, but she wanted to go on time.
Or – She cooked dinner, or she went out to a restaurant.
Yet – She owned a car, yet she didn't know how to drive it.
So – She had to go, so she called a friend to drive her.
Common problems with compound sentences include commas splices.
A comma alone is not enough to connect two sentences.
For example:
Wrong – I was tired from working late, I had to go to class anyway.
Right – I was tired from working late; I had to go to class anyway.
Right – I was tired from working late, but I had to go to class anyway.
Common problems with compound sentences include fused sentences.
Sentences cannot just run together. They must be joined with a semi-colon or a coordinating conjunction.
For example:
Wrong – My brother just graduated from high school he will attend St. Petersburg College.
Right – My brother just graduated from high school; he will attend St. Petersburg College.
Right – My brother just graduated from high school, so he will attend St. Petersburg College.
Dual construction vs. the coordinating conjunction - or when to use the comma!
When combining sentences into a compound sentence, you need a comma before the coordinating conjunction.
For example:
I like peanut butter, and I like jelly.
He eats macaroni, but he won't eat cheese.
BUT when combining two nouns or verbs, you don't need a comma.
I like peanut butter and jelly.
He eats macaroni or cheese but not both.
A special use of semi-colons - the Conjunctive Adverb
Sometimes mistaken for a FANBOY, a conjunctive adverb actually joins two sentences with a semi-colon AND has additional punctuation inside the second sentence.
For example:
I hate spinach; however, I love broccoli.
I want to graduate with honors; furthermore, I want to go to law school.
I don't want to go out tonight; besides, I have homework to do.
Some common conjunctive adverbs include accordingly, also, however, furthermore, nevertheless, consequently, finally, likewise, and meanwhile.