One
Although the test was difficult the students remained calm.
Corrected: Although the test was difficult, the students remained calm.
Why: Use a comma after an introductory dependent clause.
The team practiced hard and they won the game.
Corrected: The team practiced hard, and they won the game.
Why: Use a comma before and when it joins two independent clauses.
The movie was exciting but the ending was confusing.
Corrected: The movie was exciting, but the ending was confusing.
Why: Use a comma before but when it joins two independent clauses.
The students packed pencils notebooks and folders.
Corrected: The students packed pencils, notebooks, and folders.
Why: Use commas to separate items in a series.
Because the bus was late we missed the beginning of the concert.
Corrected: Because the bus was late, we missed the beginning of the concert.
Why: Use a comma after an introductory dependent clause.
The team practiced after school, because the tournament was close.
Corrected: The team practiced after school because the tournament was close.
Why: A comma is usually unnecessary when a dependent clause follows an independent clause.
Although the road was dangerous we continued carefully because we needed to reach town before dark.
Corrected: Although the road was dangerous, we continued carefully because we needed to reach town before dark.
Why: Use a comma after the introductory dependent clause, but not before the final dependent clause.
If you finish your homework, and check your work, you may play video games.
Corrected: If you finish your homework and check your work, you may play video games.
Why: Remove the comma between the verbs finish and check; keep the comma after the introductory dependent clause.
The students wanted to leave, they had finished the assignment.
Corrected: The students wanted to leave because they had finished the assignment.
Why: A comma cannot join two complete sentences by itself; this error is called a comma splice.
When the game ended, the players shook hands, and the crowd cheered.
Corrected: When the game ended, the players shook hands, and the crowd cheered.
Why: The commas are already correct: one follows the introductory dependent clause, and one joins two independent clauses.
Even though Jordan was tired he completed the project, and he presented it to the class.
Corrected: Even though Jordan was tired, he completed the project, and he presented it to the class.
Why: Use a comma after the introductory dependent clause and before and when it joins two independent clauses.
After the concert ended we looked for our friends but they had already left.
Corrected: After the concert ended, we looked for our friends, but they had already left.
Why: Use a comma after the introductory dependent clause and before but when it joins two independent clauses.
The new phone is expensive, it has several useful features.
Corrected: The new phone is expensive, but it has several useful features.
Why: Replace the comma splice with a comma and a coordinating conjunction.
Because the weather changed suddenly, the players left the field, and the fans hurried home.
Corrected: Because the weather changed suddenly, the players left the field, and the fans hurried home.
Why: The commas are already correct: one follows the introductory dependent clause, and one joins two independent clauses.
Gandalf is wise and mysterious he seldom explains his plans.
CORRECT: Gandalf is wise and mysterious, but he seldom explains his plans.
ERROR: Run-on / fused sentence — two complete sentences stuck together with no punctuation at all.
Because it was dark and gloomy the travelers felt weary.
CORRECT: Because it was dark and gloomy, the travelers felt weary.
ERROR: Missing comma after an introductory dependent clause — you need a comma after a long intro that starts with Because, Although, When, After, etc.
Gollum lives under the mountain, he guards the precious ring.
CORRECT: Gollum lives under the mountain. He guards the precious ring.
ERROR: Comma splice — two complete thoughts joined by just a comma. Fix with a period.
After running from the goblins Bilbo felt bewildered and exhausted.
CORRECT: After running from the goblins, Bilbo felt bewildered and exhausted.
ERROR: Missing comma after an introductory phrase — need a comma after the long opener.
Beorn is large, hairy and sometimes hospitable.
CORRECT: Beorn is large, hairy, and sometimes hospitable.
ERROR: Missing comma in a series — in a list of 3+ items, you need commas between each item.
The eagles are valiant, they saved the dwarves from peril.
CORRECT: The eagles are valiant, and they saved the dwarves from peril.
ERROR: Comma splice — two complete sentences joined with only a comma. Add FANBOYS (and) after the comma.
Although Smaug is treacherous and ominous the dwarves still want to procure their gold.
CORRECT: Although Smaug is treacherous and ominous, the dwarves still want to procure their gold.
ERROR: Missing comma after introductory dependent clause — when the sentence starts with Although, you need a comma before the main clause.
Bilbo cowered in the dark, and, waited for the tumult to end.
CORRECT: Bilbo cowered in the dark and waited for the tumult to end.
ERROR: Extra commas — don't put commas around "and" when you're just joining two verbs for the same subject.
Bilbo was bewildered, for the dwarves arrived without warning.
CORRECT: Bilbo was bewildered for the dwarves arrived without warning. OR Bilbo was bewildered, for the dwarves had arrived without warning.
ERROR: Extra comma with weak FANBOYS — "for" as a conjunction means "because" and needs a complete reason clause. When it's just explaining, you often don't need the comma at all, and students overuse it.
The goblins who live in the subterranean caves are treacherous, and ominous.
CORRECT: The goblins who live in the subterranean caves are treacherous and ominous.
ERROR: Extra comma before "and" in a compound adjective, not a compound sentence — you only need comma + FANBOYS when you have TWO complete sentences. "are ominous" is not a complete sentence by itself here.
Beorn who is solitary and venerable, is nevertheless hospitable to travelers.
CORRECT: Beorn, who is solitary and venerable, is nevertheless hospitable to travelers.
ERROR: Missing commas around nonessential clause — "who is solitary and venerable" is extra info (non-restrictive), so it needs commas on BOTH sides, not just one.