Em Dashes

Emdashes are used to set off nonessential clauses — clauses that add extra information, but are not essential to the sentence. In fact, I just used one in that last sentence. Sneaky, huh? These nonessential clauses sometimes appear in the middle of a sentence, sometimes at the beginning, and sometimes at the end. In my experience, however, the SAT only uses em dashes to separate nonessential clauses in the middle of sentences or at the end of them. For nonessential clauses at the beginning of a sentence, the SAT prefers commas.

When the correct answer choice has an em dash, most of the time it's being used to separate a nonessential clause in the middle of the sentence. When em dashes separate nonessential clauses in the middle of a sentence, there are always two em dashes - one at the beginning of the nonessential clause and one at the end. Commas can also be used to separate nonessential clauses in the middle of a sentence, but you should never combine a comma and an em dash to separate a nonessential clause. Either the clause will be separated by a comma on either side, or it will be separated by an em dash on either side.

When an em dash is used to separate a nonessential clause at the end of a sentence, there is only one em dash, which will come at the beginning of the nonessential clause. If it's used properly, then you should have a complete sentence before the em dash, and what comes after the em dash is just providing extra information.

When you see an answer choice with an em dash, you should first check if there is another em dash in the answer choice. If there is, then there's a good chance it's the right answer, and the two em dashes are separating a nonessential clause in the middle of a sentence. But you should try reading the sentence with that interpretation, and make sure it makes sense. If it's properly used, you should be able to remove everything between the em dashes and the sentence should still make sense; it will just lack the extra information provided by the nonessential clause. If this is the case, then you should select the answer choice.

Nonessential clauses are a key concept when dealing with em dashes. We covered them in more detail in the Essential v& Nonessential Clauses section. If you haven't read that section yet, or could use a refresher, now is a good time to check that page out.