Punctuation: A Crash Course

Commas help your reader follow your train of thought. Compare these two passages: 

Version 1:

For instance Sergio was struggling with his art history essay however he resisted making an appointment with the Student Learning Center because in high school his teacher shamed him whenever he tried to stay after class to clarify a question he had on the homework. Starting his first semester at college Sergio was unsure if he would be treated the same way and he was also busy juggling work and school. He took the plunge though and after an hour working with a tutor he finished his homework assignment in half the time it would have taken on his own and he felt much more confident in the skills he was developing.

Version 2:

For instance, Sergio was struggling with his art history essay. However, he resisted making an appointment with the Student Learning Center because in high school, his teacher shamed him whenever he tried to stay after class to clarify a question he had on the homework. Starting his first semester at college, Sergio was unsure if he would be treated the same way, and he was also busy juggling work and school. He took the plunge, though, and after an hour working with a tutor, he finished his homework assignment in half the time it would have taken on his own and he felt much more confident in the skills he was developing.

Which version is easier to read? 

When should you include a comma? Here are the most common places:

• Before a "FANBOY" when connecting two independent clauses. Remember the FANBOYS? Make sure to include a comma before you use one to connect complete sentences. 

Monet's paintings are beautiful but I like Van Gogh's better. ✗

Monet's paintings are beautiful, but I like Van Gogh's better. ✔

• After a dependent clause at the beginning of a sentence. When a dependent clause begins the sentence, set it off from the rest of the sentence with a comma. If your dependent clause comes at the end of the sentence, no comma is necessary.

When Van Gogh was thirty-seven he painted Starry Night. ✗

When Van Gogh was thirty-seven, he painted Starry Night. ✔

Van Gogh painted Starry Night when he was thirty-seven. ✔

• After common introductory words. Use a comma to set off common introductory words like yes, however, and well. 

Yes I'm a painter. ✗

Yes, I'm a painter. ✔

• Between three or more items of a list. Put a comma between list items. 

Caravaggio Vermeer and Rembrandt were Baroque painters. ✗

Caravaggio, Vermeer, and Rembrandt were Baroque painters. ✔

• To set off non-essential parts of a sentence. If a phrase in the middle of a sentence gives extra information, set it off with commas. For this rule to apply, the sentence must still make sense even if the non-essential elements are removed. 

Van Gogh who was born in the Netherlands died in 1890. ✗

Van Gogh, who was born in the Netherlands, died in 1890. ✔

Students, who cheat, do themselves a disservice. ✗

Students who cheat do themselves a disservice. ✔

(Notice that who cheat is necessary for the overall meaning of the sentence, so it shouldn't be set off with commas.)

Watch this video for a general overview of comma usage: