Commas and Independent Clauses

The Core Rules
    • Place a comma before “and” or “but” ONLY when they join two independent clauses.
      • An independent clause is a complete thought that has its own subject and verb and can stand alone as a sentence (e.g., She studied hard). 

  • Do NOT use a comma before “and” or “but” when they join words, phrases, or a dependent clause. 

  • Do NOT join two independent clauses with only a comma (this creates a “comma splice”). To fix a comma splice, you must use a comma plus a coordinating conjunction (like and or but), a semicolon, or a period. 

Rule 1: Using a Comma Before “And” or “But” (Joining Independent Clauses)
When AND or BUT connects two complete sentences (independent clauses) into a single compound sentence, use a comma before the conjunction.
  • Example with “and”:
    • [The rain finally stopped], and [we went for a walk].
      (Both “The rain finally stopped” and “we went for a walk” are complete sentences.)

  • Example with “but”:
    • [I wanted to stay out later], but [I had an early meeting].
      (Both “I wanted to stay out later” and “I had an early meeting” are complete sentences.)

Rule 2: NO Comma Before “And” or “But” (Joining Words, Phrases, or Dependent Clauses)

When and or but does not connect two complete sentences, leave the comma out. 

  • Connecting two words or short phrases (No comma):
    • Incorrect: She loves reading, and writing.
    • Correct: She loves reading and writing.

  • Connecting two verbs sharing the same subject (No comma):
    • Incorrect: He walked to the store, and bought some milk.
    • Correct: He walked to the store and bought some milk.

  • Connecting an independent clause to a dependent fragment (No comma):
    • Incorrect: I wanted to call you, but forgot my phone. (“forgot my phone” has no subject)
    • Correct: I wanted to call you but forgot my phone. 

Rule 3: Do Not Join Independent Clauses with Just a Comma (Comma Splice)

Never glue two complete sentences together with only a comma. 

  • Comma Splice (Incorrect):
    • The sun was shining brightly, the birds were singing.

  • How to fix it:
    • Option A (Comma + Conjunction): The sun was shining brightly, and the birds were singing.
    • Option B (Semicolon): The sun was shining brightly; the birds were singing.
    • Option C (Separate Sentences): The sun was shining brightly. The birds were singing.