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📝 English and Language Usage · Conventions of Standard English · Lesson 5 of 6 · 6 min

Sentence fragments, run-ons and comma splices: how to fix them

🔗 A sentence needs a subject, a verb and a complete thought. Too little is a fragment; two sentences jammed together is a run-on.

💡 Key idea

Fix a fragment by completing it; fix a run-on or comma splice with a period, a semicolon, comma + conjunction or a subordinator.

🧠 The idea

An INDEPENDENT CLAUSE has a subject and a verb and expresses a complete thought. A FRAGMENT is missing one of these: no subject ("Ran to the bus."), no complete verb ("The nurse checking charts."), or a dependent clause standing alone ("Because the shift ended."). Fix a fragment by adding what is missing or attaching it to a nearby sentence. A RUN-ON (fused sentence) joins two independent clauses with no punctuation: "The lab closed it reopened at noon." A COMMA SPLICE joins them with only a comma: "The lab closed, it reopened at noon." Four standard fixes: 1. a period (two sentences); 2. a semicolon; 3. a comma plus a coordinating conjunction ("closed, but it reopened"); 4. a subordinating word that makes one clause dependent ("Although the lab closed, it reopened at noon"). Words like however and therefore cannot join clauses with a comma; they need a semicolon or period before them.

✏️ Worked example

"The patient felt dizzy, she sat down quickly." Step 1: find the clauses: "The patient felt dizzy" and "she sat down quickly" each have a subject and verb, so each could stand alone. Step 2: only a comma joins them, so this is a comma splice. Step 3: choose a fix: "The patient felt dizzy, so she sat down quickly." or "Because the patient felt dizzy, she sat down quickly." Wrong fix: "The patient felt dizzy, however, she sat down." Commas around "however" still leave a splice.

📌 Takeaways

  • Fragment = missing subject, missing verb or a lone dependent clause.
  • Comma splice = two sentences joined by only a comma.
  • However and therefore need a semicolon or period before them, not a comma.

📖 Terms in this lesson

Sentence fragment: A group of words punctuated as a sentence that lacks a subject, a verb or a complete thought; for example, "Because the shift ran late."

Run-on sentence: Two or more independent clauses joined without correct punctuation or a conjunction; for example, "The bus was late I missed class."

✅ Check yourself

Question 1 of 3

Which is a sentence fragment?

  1. Study.
  2. The test was hard, but she passed.
  3. Although the test was hard.
  4. She studied late.
Show the answer and rationale

Answer: C

"Although the test was hard" is a dependent clause: the word although leaves the thought incomplete. "Study." is a complete command with an understood subject (you), and the other two are full sentences.

Question 2 of 3

Which revision corrects the comma splice? "The water was cold, we swam anyway."

  1. The water was cold we swam anyway.
  2. The water was cold, however we swam anyway.
  3. The water was cold; we swam anyway.
  4. The water was cold, and, we swam anyway.
Show the answer and rationale

Answer: C

A semicolon correctly joins two independent clauses. Removing the comma creates a fused run-on, "however" after a comma still leaves a splice, and a comma after "and" is not needed.

Question 3 of 3

"The doctor reviewing the X-rays." What does this fragment need?

  1. A subject, such as "she"
  2. A complete verb, such as "is reviewing"
  3. A conjunction at the beginning
  4. A comma after "doctor"
Show the answer and rationale

Answer: B

"Reviewing" alone is not a complete verb, so adding a helping verb ("The doctor is reviewing the X-rays") fixes it. It already has a subject (the doctor), and a comma or a conjunction would not supply the missing verb.

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