Essential vs Non-Essential Clauses

Non-essential clauses are portions of a sentence that provide extra information, but are not necessary to the sentence's meaning. For example, "Kevin, who is studying hard for the SAT, is hoping for a good score." In this sentence, "who is studying hard for the SAT" is a non-essential clause that adds extra information about Kevin. If we were to omit it from the sentence, the sentence wouldn't change in meaning, it would just be lacking a bit of extra information: "Kevin is hoping for a good score." With non-essential clauses, you should always be able to remove them from the sentence with the sentence remaining grammatically correct, and without chainging the fundamental meaning of the sentence.

Essential clauses have some similiarity to non-essential clauses; like non-essential clauses, they can generally be removed from the sentence without making it grammatically incorrect. But unlike non-essential clauses, if you remove them from the sentence you will alter the sentence's meaning. Rather than merely adding extra information, essential clauses typically help specify who or what we are talking about. For example, "The students who study hard for the SAT will score well." In this sentence, "who study hard for the SAT" is an essential clause that specifies which students will score well. If we were to omit it from the sentence ("The students will score well."), the sentence would no longer be saying the same thing. It now sounds like all students will score well, rather than just the students who study hard.

It's important to know the difference between essential and non-essential clauses because they call for different punctuation, and the SAT will test you on this. Non-essential clauses need to be separated from the rest of the sentence with punctuation, while essential clauses should not be preceded by any punctuation. For example, in the sentence "The car, which is headed east, is traveling at 60 miles per hour." the clause "which is headed east" is non-essential, and so it is separated from the rest of the sentence with commas. Conversely, in the sentence "The car that is headed east is traveling toward Boston." the clause "that is headed east" is essential to specify which car is being talked about, and so it is not preceded by any punctuation.

Non-essential clauses often show up at the beginning of a sentence, in which case they are normally describing (aka "modifying" in grammar terms) the subject of the sentence. For example, take the sentence "Hoping to get into a good college, Katherine prepared thoroughly for the SAT." In this sentence, "hoping to get into a good college" is a non-essential clause that modifies the subject of the sentence, "Katherine." If we were to remove it from the sentence, the sentence would still make sense: "Katherine prepared thoroughly for the SAT." Non-essential clauses at the beginning of a sentence should be separated from the rest of the sentence with a comma.

• "Tired from his run yesterday, Jack collapsed on his couch."
• "Afraid of failing the test, Caroline stayed up all night studying."
• "Walking to the store, Jim stopped to buy a newspaper."
• "An opera lover, Janet went to see the Metropolitan Opera."

Non-essential clauses can also show up in the middle of a sentence. For example, take the sentence "George, who loves burritos, is going to Chipotle." The non-essential clause in this sentence is "who loves burritos". Again, we could remove it from the sentence while maintaining a complete sentence with the same meaning: "George is going to Chipotle."

• "Jack, tired from his run yesterday, collapsed on his couch."
• "Caroline, afraid of failing the test, stayed up all night studying."
• "Jim, walking to the store, stopped to buy a newspaper."
• "Janet, an opera lover, went to see the Metropolitan Opera."

Non-essential clauses can also show up at the end of a sentence, like in the sentence "He adopted a german shepherd - a dog breed known for its loyalty." Non-essential clauses at the end of a sentence can be separated from the rest of the sentence with a comma or an em dash.

• "Jack collapsed on his couch, tired from his run yesterday."
• "Caroline stayed up all night studying, afraid of failing the test."
• "Jim stopped to buy a newspaper, hoping to learn more about the election."
• "Janet went to see Best In Show, a movie about dog competitions."

There are various types of words that often lead off essential and/or non-essential clauses. Some can apply to both, while others only apply to one. Here are some common types of words that can lead off dependent clauses:

• Relative pronouns
  • Words like "that", "which", "who", "whom", "whose", "when", "where", etc.
  • Example: "Jack, who is training hard, plans to run a marathon."
• Verbs ending in "-ing"
  • Example: "Training hard, Jack hopes to break 3 hours in the marathon."
• Verbs ending in "-ed"
  • Example: "Jack collapsed on his couch, tired from his training run."
• Adjectives
  • Example: "Jack, sore from his run yesterday, went down the stairs gingerly."

While the words "that" and "which" are often used similarly to lead off dependent clauses, they are not interchangeable. "That" is used to specify, while "which" is used to add additional information. Therefore, you almost never want a comma before the word "that" because it is the start of an essential clause. On the other hand, when you use "which" to add additional information, you want a comma before it. For example, you would say "I bought the car that was cheapest" (no comma), or you might say "I bought the white Corolla, which happened to be the cheapest car on the lot" (with a comma).

We just saw that the words "that" and "which" can tell us whether a clause is essential or non-essential. But as we saw above, there are many other ways to start off dependent clauses. So how do you we know if a clause is non-essential (and should be punctuated) or essential (and should not be punctuated)? The key question to ask is whether omitting that clause would change the sentence's meaning. In essential clauses, that clause is needed to specify one of the nouns we are talking about, whereas non-essential clauses just give additional information about something the sentence is talking about. For example, "The athlete who trains the hardest will win the race" contains the essential clause "who trains the hardest", which is necessary to specify which athlete we are talking about. Whereas in the sentence "The race was won by Eliud Kipchoge, who trained the hardest" we are already talking about a specific athlete, so the clause "who trained the hardest" just provides additional information about him.