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Course: Digital SAT Reading and Writing > Unit 5
Lesson 7: Boundaries: SupplementsGrammar guide: Supplements
A guide to supplementary phrases on the SAT.
What are supplements?
Supplements are words, phrases, and relative clauses that add extra information to a sentence, often for the purpose of description or elaboration. There are two main types of supplements:
Essential elements are necessary for the sentence to function and don't require punctuation.
Nonessential elements are not necessary for the sentence to function. They must be separated from the main sentence by punctuation.
The SAT focuses on whether supplements should be separated from the rest of the sentence by punctuation, as well as what punctuation marks should be used. These conventions may be tested in Boundaries questions that you encounter on test day.
How are supplements punctuated?
There are several factors that govern how supplements should be treated within a sentence. Let's look at each in turn.
Essential or nonessential
The first question is whether a given supplement should be punctuated. Try reading the sentence without the supplemental information.
- If the sentence no longer makes sense, then the supplement is an essential element. No punctuation should be used.
- If the sentence still makes sense, then the supplement is nonessential. The supplement must be separated from the rest of the sentence by punctuation.
Position in the sentence
Once you determine a supplement is nonessential, you must decide how to punctuate it.
- If the supplement begins or ends the sentence, it only requires one punctuation mark (between the supplement and the rest of the sentence).
- If the supplement comes in the middle of the sentence, it requires punctuation on both sides.
Type of punctuation
Nonessential elements can be separated from the rest of a sentence using three different types of punctuation marks:
- Commas (,)
- Parentheses ()
- Dashes (—)
In formatting supplements, these punctuation marks are basically interchangeable. However, there is one important rule: the same type of punctuation must appear before and after a nonessential element.
In other words, we don't want to be mixing different punctuation marks together.
How to identify supplements questions
When approaching boundaries questions, it's important to identify which Standard English conventions are being tested.
You may want to look for errors in supplements if
- the choices add or remove commas, but not conjunctions
- the choices include multiple types of punctuation, like commas and dashes
If you don't see either of these features, then the question likely doesn't deal with supplements.
Let's look at a supplements question now:
Top tips
Be consistent!
SAT questions will often include just one side of a nonessential element in the underlined portion of the sentence. Be sure to check the other side of the element for consistency: the same punctuation mark should be used on both sides!
Don't worry about the difference between commas, parentheses, and dashes
While commas, parentheses, and dashes are sometimes better in particular contexts, the SAT won't test you on these minor differences. In other words, you'll never be asked to choose between two types of punctuation marks if the choices don't create other grammar errors. So don't sweat it!
Don't pair semicolons or colons!
Commas, parentheses, and dashes are the only options when separating a nonessential element from the rest of the sentence. We should never use two semicolons or colons around a nonessential element.
Your turn
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- SAT: While commas, parentheses, and dashes are sometimes better in particular contexts, the SAT won't test you on these minor differences
Also SAT: Proceeds to bash my brain with the difference between colons, semicolons, and dashes(56 votes)- think a semicolon is like a fullstop
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