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SAT Grammar: Boundaries — Supplements

How to punctuate and identify supplementary phrases, appositives, and non-essential elements in sentences

Supplements questions on the SAT test your ability to properly enclose non-essential information—words, phrases, and clauses that add detail or clarification but aren’t required for grammatical completeness.

What Are Supplements?

Definition: Supplements are descriptive words, phrases, and relative clauses that provide extra information. They can be removed without changing the base meaning or grammatical completeness of the sentence.

Common Types: Appositive phrases, non-restrictive clauses, parenthetical expressions.

Formula:
A supplement must be set off by matching punctuation (commas, dashes, or parentheses). Example markup: main clause, supplement, rest of main clause
Key Rule: A supplement is removable! If you cross it out, the sentence must still be grammatically correct and make sense.

How to Punctuate Supplements (Commas, Dashes, Parentheses)

  • Commas—most common, used before and after non-essential phrases/appositives/clause: The book, a bestseller, was released last year.
  • Dashes—used for emphasis or abrupt pauses: Her study habits—always intense—led to success.
  • Parentheses—used for side notes: She gave him her answer (yes!) immediately.
Be consistent—never mix punctuations. If you start a supplement with a comma, use another comma to end it. Dash to dash, parenthesis to parenthesis.

Common SAT Pitfalls & Tips

  • ❌ Don’t use only one comma or dash! Both sides of a supplement must be set off by punctuation.
  • ❌ Don’t use semicolons or colons around supplements.
  • ❌ Don’t separate two complete sentences with a comma and supplement—use a period or semicolon.
  • ✅ If you can remove a section and the sentence still makes sense, it’s a supplement—check punctuation!
  • ✅ The SAT never asks you to choose between dashes, commas, or parentheses unless another error is present—focus on grammatical correctness first.

Fully Worked SAT-Style Examples

Example 1:

Torsha, a fan of celebrity gossip, loves watching The Wendy Williams Show.

Step-by-step: By removing “a fan of celebrity gossip”, the sentence is still complete. It’s an appositive—set off with two commas.
Example 2:

Her new book—a combination of fiction and memoir, poetry and criticism—serves as a testament to her versatility.

Step-by-step: The dash-enclosed section is not required for grammar; without it, “Her new book serves as a testament…” is still correct.
Example 3:

Mycology, the study of fungi, is a rapidly expanding science.

Step-by-step: “the study of fungi” is a clarifying supplement—remove it, and the sentence is still complete. So use commas.
Example 4:

The restaurant's specialty (which diners travel far to experience) is a traditional seafood stew.

Step-by-step: “which diners travel far to experience” is extra detail; parentheses are used for side notes.
Example 5:

Professor Lee—a leader in the field—was interviewed by the local news.

Step-by-step: Dash supplement for emphasis; “a leader in the field” could be removed without affecting grammar.

Test-Day Strategies

1. Identify removable information
If deleting a phrase doesn’t change basic sentence meaning, use punctuation to enclose it.
2. Match punctuation
If a supplement starts with a comma/dash/parenthesis, it must end with the same.
3. Don’t confuse supplements with required information
Essential phrases are not set off by punctuation.
4. Review for fragments
Don’t use periods, semicolons, or colons to enclose supplements; these only connect complete thoughts.

Quick Reference Table: Punctuating Supplements

Type Punctuation Example
Appositive (non-essential) Commas (most common) My friend, a tennis champion, won the match.
Parenthetical detail Parentheses (side notes) The answer (if you can believe it) was correct.
Emphasized supplement Dashes (for emphasis) The stars—all visible tonight—filled the sky.

Key Takeaways

  • Supplements are optional, removable elements. If you cross it out, the sentence must still be complete.
  • Enclose supplements with commas, dashes, or parentheses—but use matching marks!
  • Never use a period, colon, or semicolon to enclose supplements.
  • The SAT tests: can you identify the non-essential part and punctuate it correctly?
  • The SAT does not ask you to choose between comma/dash/parenthesis unless another error is present.
  • If in doubt, try removing the phrase! If the sentence works, treat it as a supplement.

When in doubt, cross out the extra phrase. If you have a complete sentence left, enclose it with proper punctuation—commas, dashes, or parentheses!