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Writing lesson · Sentence writing
Complete Sentences: Fix Fragments and Run-On Sentences
Check that every sentence has a doer, an action and a finished thought. Fix fragments and run-ons, practise editing, and write a short paragraph.
The idea
A complete sentence has three things: a subject (who or what the sentence is about), a verb (what the subject does or is) and a finished thought. "The goalie caught the puck." has all three. Readers can stop at the period and feel nothing is missing.
A fragment is a piece of a sentence that is missing one of those parts. "Ran across the ice." has no subject: who ran? "The tall goalie in the red mask." has no verb: what did the goalie do? "When the buzzer rang." has a subject and a verb, but the thought is not finished: what happened when it rang?
A run-on sentence is the opposite problem. Two complete sentences are pushed together with nothing strong enough between them: "The buzzer rang we cheered." A comma alone is not strong enough either: "The buzzer rang, we cheered." You can fix a run-on in two ways. Split it into two sentences with a period, or join the ideas with a comma and a joining word such as and, but or so: "The buzzer rang, and we cheered."
Fragments are not always mistakes. Writers sometimes use a short fragment on purpose, such as "Silence." or "Not today." For schoolwork and for most of your own writing, check each sentence first. Make it complete unless you are certain a fragment is the best choice.
See the difference
A first attempt
Last Saturday at the community pool. My cousin and I swam for an hour then we ate lunch on the deck. Ate fries and fruit. The lifeguard blew her whistle, everyone left the water. Because it was time for adult swim.
Last Saturday, my cousin and I went to the community pool. We swam for an hour, and then we ate lunch on the deck. We ate fries and fruit. The lifeguard blew her whistle, and everyone left the water because it was time for adult swim.
Why this works: The weak version has three fragments (the opening phrase, "Ate fries and fruit." and "Because it was time for adult swim.") and two run-ons (swam for an hour then we ate; whistle, everyone left). The strong version gives every sentence a subject, a verb and a finished thought, and it uses a comma with and to join ideas that belong together.
Worked examples
Example 1 · Add the missing subject
Fix this fragment: "Jumped over the puddle."
- Ask: who or what jumped? The word group has a verb (jumped) but no subject.
- Add a subject that fits: the girl, my dog, we.
- Check that the sentence now makes sense on its own.
My dog jumped over the puddle.
Example 2 · Add the missing verb
Fix this fragment: "The old wooden bridge near our cottage."
- Ask: what did the bridge do, or what is it like? There is a subject but no verb.
- Add a verb and the rest of the idea.
- Read it aloud to check that it sounds finished.
The old wooden bridge near our cottage creaks when we walk on it.
Example 3 · Finish the thought
Fix this fragment: "Because the bus was late."
- Because makes the reader wait for the result. Ask: what happened because of that?
- Add the result, with a comma between the two parts, or join the reason to a main sentence.
- Check that the sentence stands alone.
Because the bus was late, we missed the first song. (Another correct version: We missed the first song because the bus was late.)
Example 4 · Fix a run-on two ways
Fix this run-on: "Mia packed her skates she forgot her helmet."
- Find where one complete idea ends: Mia packed her skates.
- Option A: end the first sentence with a period and start a new one with a capital letter.
- Option B: join with a comma and a joining word that matches the meaning. The second idea is a surprise, so use but.
Option A: Mia packed her skates. She forgot her helmet. Option B: Mia packed her skates, but she forgot her helmet.
Common mistakes
Why this fails: This is a comma splice, a kind of run-on. A comma is not strong enough alone. Add a joining word (It was cold, so we wore mittens) or use a period.
Why this fails: Length does not make a sentence. "Walking along the beach with my grandparents on a sunny afternoon." is long but has no complete verb or doer. Test for subject, verb and finished thought.
Why this fails: "Birds sing." is complete: birds is the subject and sing is the verb. Short sentences can be complete.
Why this fails: These words promise more information. "When the rain stopped." leaves the reader waiting. Finish with what happened.
Why this fails: Use the joining word that matches the idea. And adds, but shows a difference, and so shows a result. Sometimes a period is the best fix.
Foundation
Foundation practice
Decide whether each group of words is a complete sentence.
1. Which group of words is a complete sentence?
- Running down the hill.
- The tall pine tree behind our school.
- Because it started to snow.
- My brother builds model rockets.
2. "Found a wallet on the sidewalk." What is missing?
- A verb
- A subject
- A capital letter
- Nothing; it is complete
3. "The little yellow canoe on the quiet lake." What is missing?
- A subject
- A period
- A verb
- A joining word
4. Which one is a run-on sentence?
- We cleaned the kitchen, and then we watched a movie.
- I love soup it keeps me warm.
- After dinner, Dad washed the dishes.
- Our class visited the library on Tuesday.
5. Which fix turns "Fish swim ducks paddle." into correct writing?
- Fish swim, ducks paddle.
- Fish swim. Ducks paddle.
- Fish swim ducks, paddle.
- Fish. Swim ducks paddle.
Practice
Practice practice
Fix fragments and run-ons while keeping the meaning.
6. Which choice fixes the fragment "Played soccer at recess."?
- Played soccer at recess with Jordan.
- Soccer at recess.
- Played soccer at recess, we.
- Jordan and I played soccer at recess.
7. Which choice fixes "The soup was hot I waited for it to cool" using a joining word?
- The soup was hot, I waited for it to cool.
- The soup was hot, so I waited for it to cool.
- The soup was hot so, I waited for it to cool.
- The soup was hot but I waited, for it to cool.
8. Which choice completes the fragment "When we reached the top of the hill"?
- we could see the whole town.
- and the whole town.
- the whole town below.
- because we could see.
9. Which joining word best fits? "I wanted to ride my bike, ___ it was raining."
- so
- and
- but
- or
10. Which group of words in this passage is a fragment? "Our class planted a garden. Tomatoes, peppers and herbs. We water it every day."
- Our class planted a garden.
- Tomatoes, peppers and herbs.
- We water it every day.
- All three are complete
Challenge
Challenge practice
Edit whole paragraphs and write your own.
11. Which edit fixes every problem in this sentence? "Because the ice was thin. We stayed on the shore, the lake looked beautiful."
- Because the ice was thin, we stayed on the shore. The lake looked beautiful.
- Because the ice was thin we stayed on the shore, the lake looked beautiful.
- Because the ice was thin. We stayed on the shore. The lake looked beautiful.
- Because the ice was thin, we stayed on the shore, the lake looked beautiful.
12. How many problems are in this passage? "Dad grilled burgers. Corn on the cob. We sat outside the sun was low."
- Zero
- One
- Two
- Three
13. Which sentence is complete and correctly punctuated?
- Since we had finished our homework.
- Mom picked us up, we went for ice cream.
- Mom picked us up, and we went for ice cream.
- Went for ice cream after school.
14. A friend's paragraph has three fragments and two run-ons. What is the best first step?
- Add a comma after every sentence.
- Read each sentence aloud and ask for a subject, a verb and a finished thought.
- Replace every period with and.
- Make every sentence as long as possible.
15. Fix this paragraph so every sentence is complete: "On the first day of winter break. We built a snow fort it was huge. Used shovels and buckets. Because the snow was perfect for packing."
Your turn to write
Write a paragraph of 5–7 sentences about a time you played a game or sport with friends or family. First write a fast draft without worrying about sentences. Then check every sentence for a subject, a verb and a finished thought. Fix at least one fragment or run-on if you find one, and use a comma with and, but or so at least once.
Helpful sentence starters
- Last weekend, we …
- Before the game, …
- My team …
- When the whistle blew, …
- In the end, …
Write in a notebook or a document. The model and checklist are available without signing in.
Check and improve
- Every sentence has a subject (who or what).
- Every sentence has a verb (what happens).
- Every sentence is a finished thought I could stop at.
- I fixed run-ons with a period or with a comma and a joining word.
- I used a comma before and, but or so when joining two full ideas.
- If I kept a short fragment, I did it on purpose and it works.
- I read my paragraph aloud and listened for places where I ran out of breath.
This checklist is for parent-and-child self-review. No automatic writing score is assigned.
Answer key
- 1. My brother builds model rockets.
It has a subject (my brother), a verb (builds) and a finished thought. The others are fragments: the first has no subject, the second has no verb, and the third leaves the thought unfinished. - 2. A subject
Found is a verb and the words tell what happened, but we do not know who found the wallet. A verb is already there, a capital letter is already there, and the sentence is not complete. - 3. A verb
The words name a canoe and where it is, but nothing tells what the canoe does. A subject is already there (the little yellow canoe), and a period would not fix the missing action. - 4. I love soup it keeps me warm.
Two complete ideas (I love soup; it keeps me warm) run together with no punctuation or joining word. The other three are correctly built sentences. - 5. Fish swim. Ducks paddle.
Each idea is complete, so a period and a capital letter separate them. A comma alone makes a comma splice, a comma in the wrong spot does not help, and the last choice breaks the words into fragments. - 6. Jordan and I played soccer at recess.
The fragment needs a doer. Adding Jordan and I as the subject makes it complete. Adding more words after the verb still leaves no subject, and the other choices stay broken. - 7. The soup was hot, so I waited for it to cool.
So shows a result, and the comma goes before it. A comma alone is a comma splice. Putting the comma after so or inside the second idea puts it in the wrong place, and but does not fit the meaning. - 8. we could see the whole town.
The opener needs a subject and verb that tell what happened. We could see the whole town does that. The other choices add more fragments or another unfinished reason. - 9. but
The rain is the opposite of what you hoped, so but is the best match. So would make the rain the result of wanting to ride, and and or do not show the problem. - 10. Tomatoes, peppers and herbs.
This list names things but has no verb to say what they do or what happens to them. The first and third each have a subject, a verb and a finished thought. - 11. Because the ice was thin, we stayed on the shore. The lake looked beautiful.
Joining the Because group to the main idea with a comma fixes the fragment, and a period fixes the comma splice. The other choices leave the fragment or the comma splice, or both. - 12. Two
"Corn on the cob." is a fragment with no verb, and "We sat outside the sun was low" is a run-on. Dad grilled burgers is correct, so there are exactly two problems. - 13. Mom picked us up, and we went for ice cream.
Two complete ideas are joined with a comma and and. The first choice is an unfinished thought, the second is a comma splice, and the fourth has no subject. - 14. Read each sentence aloud and ask for a subject, a verb and a finished thought.
Testing one sentence at a time shows exactly what is missing. Commas, extra ands and longer sentences do not fix missing parts and can create new run-ons. - 15. Sample answer: On the first day of winter break, we built a snow fort, and it was huge. We used shovels and buckets. The snow was perfect for packing.
Answers can vary. A good revision gives the opening phrase a main sentence, fixes the run-on with a period or a comma and a joining word, adds a subject to the second fragment (we) and finishes or joins the Because idea.