SHSAT: Sentence boundaries: joining complete thoughts
Learn to spot complete thoughts, the correct ways to join them, and the comma splice, the error behind most wrong answers in this question type.
When two complete thoughts sit side by side, what can correctly hold them together?
Short answer
A period, a semicolon, a comma plus a joining word such as and, but or so, or a colon when the second thought explains the first. A comma by itself is never enough.
Know first: Subjects and verbs
Step 1 of 5
Spot the complete thoughts first
A complete thought, also called an independent clause, has a subject and a verb and can stand alone as a sentence: The bus arrived.
A dependent clause starts with a word like because, when, although or if. It has a subject and verb but can't stand alone: Because the bus arrived. Written on its own, it's a fragment. A phrase with no subject or no full verb is a fragment too: Running for the bus. Add both: Running for the bus, Ana dropped her keys.
Most sentence-boundary questions come down to one decision: are there two complete thoughts here, and if so, what is holding them together?
| Method | Example |
|---|---|
| Period | The rain stopped. We went outside. |
| Semicolon | The rain stopped; we went outside. |
| Colon, when the second thought explains the first | The plan changed: the bridge was closed for repairs. |
| Comma + and, but, or, so, yet | The rain stopped, so we went outside. |
| Make one part dependent | When the rain stopped, we went outside. |
Wrong: The rain stopped, we went outside.
Right: The rain stopped, so we went outside.
A comma can join two complete thoughts only when a joining word like so comes with it.
Step 2 of 5
Watch out for however
Words like however, therefore and for example are transitions. They connect ideas, but they can't join two complete thoughts the way but or so can. They need a semicolon or a period in front of them.
Worked example: A sentence with however
Which revision correctly punctuates "The museum was free on Sundays, however, few people knew"?
- AThe museum was free on Sundays; however, few people knew.
- BThe museum was free on Sundays, however few people knew.
- CThe museum was free on Sundays however, few people knew.
- DThe museum was free on Sundays, however, few people knew.
- 1
Find the complete thoughts
The museum was free on Sundays and few people knew each have a subject and a verb. That's two complete thoughts.
- 2
Check what joins them
However is a transition, not a joining word, so the comma before it creates a comma splice.
- 3
Fix the boundary
Put a semicolon before however and a comma after it. That's choice A. Choice D is the unchanged comma splice, and B and C each still have only a comma, or nothing, at the boundary.
Answer
A. The museum was free on Sundays; however, few people knew.
Step 3 of 5
Try it yourself
Find the wrong step
A student fixes this sentence: The game ended late, the bus waited for the team.
- 1
Finds two complete thoughts: The game ended late and the bus waited for the team.
- 2
Adds because and a period: Because the game ended late. The bus waited for the team.
What went wrong
Adding because makes the first part dependent. The period then cuts it off from the main clause, so it becomes a fragment.
- 3
Decides the sentence is now correct.
The fix
Keep the two parts in one sentence: Because the game ended late, the bus waited for the team. Or use a joining word: The game ended late, so the bus waited for the team.
Check yourself · Question 1
Which sentence is correctly punctuated?
Answer: B
A semicolon correctly joins two complete thoughts. A is a comma splice, C runs the two thoughts together, and D puts an extra comma after and.
Check yourself · Question 2
Which revision joins "The trail was steep. We reached the top." and shows contrast?
Answer: B
But shows contrast, and a comma plus but correctly joins two complete thoughts.
Trap answer: The trail was steep, so we reached the top.
Correct punctuation, wrong meaning
- Why it looks right
- The punctuation is perfect, so it looks like a safe choice.
- Why it's wrong
- So means the steep trail caused you to reach the top. The question asks for contrast.
- The right answer
- The version with but gets both the punctuation and the meaning right.
Common mistake
Fixing a comma splice by deleting the comma.
- Why it's tempting
- Removing the comma that caused the problem looks like the obvious fix.
- Do this instead
- Deleting the comma turns a comma splice into a run-on. Keep the comma and add a joining word, or replace it with a period or a semicolon.
Step 4 of 5
What to remember
Remember
- Count the complete thoughts before you look at the punctuation.
- Join two complete thoughts with a period, a semicolon, a comma plus and, but, or, so or yet, or a colon when the second explains the first.
- Choose the joining word that matches the meaning: but for contrast, so for a result.
Step 5 of 5
Practice on a real question
Use what you just learned on this question, then check the explanation.
In your own words
In the practice question, how many complete thoughts were there, and what was wrong with the choice that used only a comma?