A comma splice is a run-on with a comma at the border: “It rained, we stayed inside.” In Commas in Compound Sentences the comma came with a conjunction; here it is alone, and alone it can’t do the job.
Key idea
A comma alone can’t join two independent clauses. Words like however, then, therefore and also are not conjunctions, so a comma before them still makes a splice.
Why it works
A comma tells the reader the sentence continues as one thought; a new subject right after it surprises them. Strunk’s fifth rule (1918) is “Do not join independent clauses by a comma.” He allowed one exception: “If the clauses are very short, and are alike in form, a comma is usually permissible,” as in “Man proposes, God disposes.” In school writing, use a stronger joint.
Worked example: Spot the splice
“The movie was long, we enjoyed it anyway.”
- Cover the comma. “The movie was long.” Whole. “We enjoyed it anyway.” Whole.
- Two independent clauses with only a comma between them: a comma splice.
- One fix: add a conjunction.
Answer: The movie was long, but we enjoyed it anyway.
Worked example: The however trap
“It rained, however we played outside.”
- However is a conjunctive adverb, not a conjunction.
- So the comma is still joining two independent clauses alone.
- Put a semicolon before however and a comma after it.
Answer: It rained; however, we played outside.
Worked example: Not a splice
“When it rained, we played inside.”
- “When it rained” is a dependent clause.
- A comma after an opening dependent clause is right.
Answer: Correct as written.
Common mistake
Joining clauses with a comma and a word like however or then: “We ate dinner, then we washed the dishes.” Fix it with and then, a semicolon, or a period.