The comma that never belongs: splitting a subject from its verb
"Every student who finished the summer research program, received a certificate." That comma is doing nothing but breaking the sentence.
Why it happens
Long subjects are tiring to read, and a comma feels like permission to rest. But nothing separates a subject from its verb — the longer the subject, the stronger the urge, and the more often the SAT tests it.
See the trap
"Every student who finished the program ___ received a certificate."
✗ The trap: "program, received" — the comma cuts the subject off from its own verb.
✓ The fix: "program received" — no punctuation. The subject runs straight into the verb.
How to actually fix it
- Strip the sentence to its bare subject and verb: "student received".
- Would you put a comma between those two words? Never.
- Adding words to the subject does not change that answer.
Made this mistake on a real question?
Practice Standard English Conventions questions here. Miss one and it is logged with the exact error, then brought back until you beat it.
Practice Standard English Conventions →FAQ
What if there is an interrupting phrase in the middle?
Then you need two commas, not one — "Every student, having finished the program, received a certificate." A single comma is the error; a matched pair is fine.
How do I stop repeating this mistake?
Reading the explanation isn't enough — your brain needs to beat the trap on a fresh question. Practice the skill in the kaoshen.co question bank: miss one and it is logged with the exact error, then brought back to you three days later and again after fourteen.