Reading and Writing · 18 · Sentence Rules
Independent Clauses and Non-Essential Information
Notes
Key points
- Non-essential info can be lifted out; the sentence keeps its meaning.
- Wrap it in matching marks: two commas, two dashes, or two parentheses.
- Essential info (tells you which one) takes no commas.
- which → non-essential, commas. that → essential, no commas.
- At the start or end of a sentence, one mark does it: “…, a city in Peru.”
- Remove the wrapped part: what's left must be a complete sentence.
Rules
Non-essential phrase: commas on both sides.
Lima, the capital of Peru, sits on the coast.
Lima, the capital of Peru sits on the coast.
Matching marks: comma with comma, dash with dash.
The fossil — nearly complete — was found in 2019.
The fossil, nearly complete — was found in 2019.
Essential “that” clauses take no commas.
The novel that won the prize sold well.
The novel, that won the prize, sold well.
Common traps
- Seeing one comma and forgetting its partner on the other side.
- Putting commas around a phrase that identifies which one you mean.
SAT tip
Read the sentence without the extra phrase: if it still works, the phrase needs a matching mark on each side.
Test yourself
10 official SAT questions on Independent Clauses and Non-Essential Information, easiest first.