Comma splice: why the SAT never lets a comma join two sentences
"The experiment failed, the sample was contaminated." That comma is the single most tested punctuation error on the SAT — and it is wrong 100% of the time.
Why it happens
Both halves sound like one connected thought, so a comma feels like the right amount of pause. But the SAT tests structure, not pauses: if each side could stand alone as a sentence, a comma alone is never strong enough to hold them together.
See the trap
Which choice conforms to the conventions of Standard English? "Marisol rewrote the opening ___ it now begins with the storm."
✗ The trap: "chapter, it now begins" — both sides are full sentences, so the comma cannot join them.
✓ The fix: "chapter; it now begins" — or a period, or "chapter, and it now begins". Semicolon, period, or comma + FANBOYS.
How to actually fix it
- Cover everything left of the punctuation. Is what remains a complete sentence?
- Cover everything right of it. Same question.
- If both answers are yes, a bare comma is out — you need a semicolon, a period, or a comma plus and/but/or/so/for/nor/yet.
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
Is a comma splice ever acceptable?
In literary writing, sometimes. On the SAT, never — the test only asks about Standard English conventions, and there the answer is always no.
What if the second sentence starts with 'however'?
That makes it worse, not better. "However" is not a conjunction, so "it failed, however the data was useful" is still a splice. Use a semicolon before it and a comma after.
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.