This time let’s focus on conjunctions. Conjunctions are words that join other words, clauses, or phrases. Grammar consists of three kinds of conjunctions: coordinating, correlative, and subordinating.
A coordinating conjunction joins words, clauses, or phrases that are equal either in weight or function. Here’s a list of common coordinating conjunctions:
Punctuating a coordinating conjunction depends on what the conjunction is joining.
*The movie was long and boring. And is the conjunction joining two adjectives. No punctuation is needed.
*The cupcake was delicious but fattening.
*We meandered down a steep, curvy, and overgrown path. And joins a series in this sentence. The comma here is the controversial Oxford comma. Some people delete it now. I don’t.
When a coordinating conjunction joins two sentences, punctuate with a comma before the conjunction.
*The Girl Scouts may sell cookies in front of the grocery store, or they may choose to sell at the ballgame. The previous sentence has a subject and verb on both sides of the conjunction or. The two smaller sentences are joined by a comma and a conjunction.
*The Girl Scouts may sell cookies in front of the grocery store or at the ballgame. In this sentence, or joins the two prepositional phrases in front of the grocery store and at the ballgame. No comma is needed because or is joining two phrases, not two sentences.
To punctuate sentences correctly, a writer should know which words are subjects and verbs and prepositions–exactly why we’re studying the parts of speech!