Grammar and Punctuation Rules

A phrase is a cluster of two or more words that do not form a complete thought. Usually, phrases are either a subject with no verb or a verb with no subject:

• Jumping up and down
• The orange cat

A clause has a subject and a verb, and it can be a complete sentence or part of a complete sentence.

• The plane left this morning. (this is a clause that forms a complete sentence)
• While I was driving (this is a clause that is an incomplete sentence on its own, but it could be part of a complete sentence if paired with another clause)

An independent clause is a group of words that contains a subject and verb and expresses a complete thought. In other words, an independent clause is a complete sentence.

• I couldn't sleep last night.

A dependent clause has a subject and a verb, but it is not a complete sentence. It is a part of a sentence that needs more information to be complete (it depends on another clause or phrase to become a complete sentence).

• Because I ate chocolate before bed (this has a subject and a verb, but it needs more information to present a complete thought)
• Because I ate chocolate before bed, I couldn't sleep last night. (This is a complete sentence that is made up of two clauses, and independent clause and a dependent clause.

A compound sentence has at least two independent clauses, and they should be separated by a comma and a coordinating conjunction.

A complex sentence contains an independent clause and at least one dependent clause, but they are not separated by a comma.

A conjunction is a part of speech that connects words, phrases, or clauses, and a coordinating conjunction connects two words, phrases, or clauses of equal importance or having the same grammatical structure.

How to use commas with compound and complex sentences:

Step 1: Identify if it is a compound or complex sentence. Are there two independent clauses? A reminder that an independent clause contains a subject and a verb, and it can stand by itself as a sentence. Examples are below:

I went grocery shopping.

I came home with a new cat.

Both of these clauses have a subject and a verb, and both can stand alone as their own sentence. If they are brought together, they make a compound sentence:

I went grocery shopping, but I came home with a new cat. 

In this sentence, the coordinating conjunction is "but."

There are seven common coordinating conjunctions: for, and, nor, but, or, yet, and so. These can be remembered using the memory aid FANBOYS.

Introductory phrases and words are dependent parts of a sentence that "set the stage" for the independent clause (complete idea/sentence) following it. Use commas to set off the introductions.

• Yesterday, I went shopping with my aunt.
• After the meeting, we went out for lunch. 
• Without thinking, she jumped off of the cliff into the dark water.
• No, I do not want to watch that movie.
• In contrast, the results of the second study suggest an entirely different conclusion.

A parenthetical phrase or clause is like a side comment--it's a part of a sentence that adds information but is not essential for making the sentence complete. Parenthetical phrases or clauses are set off by commas.

• My little sister, who is ten years old, likes hunting for worms.

One could remove the phrase "who is ten years old," and the sentence would still be complete.

If you can add the words "by the way" to the phrase or clause into the essential part of the sentence, chances are it is parenthetical. 

• The weather today, which (by the way) is beautiful, makes me want to take a long walk.

The example below demonstrates the difference between the use of a comma with a restrictive (essential) phrase or clause and a nonrestrictive (parenthetical, non-essential) phrase or clause.

• The scooter that has a flat tire is parked in the lot. (Restrictive: indicates more than one scooter)
• The scooter, which has a flat tire, is parked in the lot. (Nonrestrictive: adds non-essential information about the only scooter)