Restrictive and Non-restrictive clauses 101.

What are restrictive and non-restrictive clauses?

You may remember from eighth grade grammar the terms restrictive and non-restrictive clauses, but do you remember what they are? The distinction between these two types of clauses seems to cause writers some trouble. Just ask Google! Here, I will give you a short lesson on these grammar tools and how to use them in your formal writing. Simply put, restrictive and non-restrictive clauses are relative clauses that add information to the noun of a sentence. The difference between them is that restrictive clauses restrict, or add necessary meaning, to the noun. Without the restrictive clause, the meaning of the sentence becomes unclear because the noun is no longer defined (i.e., restricted).
Below are example sentences from my graduate school research with and without a restrictive clause.

“The mitomycin C derivative that cross-links DNA is too unstable to isolate.”

When the clause after that is removed you get

“The mitomycin C derivative is too unstable to isolate.”

The second simple sentence may be accurate, but without context the reader can no longer be certain which derivative is being discussed. The definite article “the” signals that I am referring to a specific derivative, but the object is unclear without another sentence or the restrictive clause.

In contrast to the restrictive clause, which restricts the noun and gives necessary information to the meaning of the sentence, the non-restrictive clause does not restrict the noun and is not necessary for reader understanding. Below is an example with a non-restrictive clause.

“Mitomycin C, which is activated in situ by two-electron reduction to a reactive intermediate, is a non-specific anticancer prodrug.”

Notice that the non-restrictive clause gives information about the noun, but it doesn’t restrict the noun.

“Mitomycin C is a non-specific anti-cancer prodrug.”
The sentence has the same meaning, but with less information.

Is it restrictive or non-restrictive?

In order to identify if a clause is restrictive or non-restrictive, use the following clues.

In American English commas and the relative pronoun used (that, which) signal if the clause is restrictive or non-restrictive. Notice above that in my example of a restrictive clause I used the relative pronoun that, and in the non-restrictive clause, I used “which”. Another signal of a non-restrictive clause is that it must be enclosed by commas.

The final test to determine if the clause is restrictive or non-restrictive is to remove the clause completely as I did above.

Does the noun become ambiguous to the reader? Could the sentence be misinterpreted? If the answer is “Yes”, add the clause back to avoid confusion.

Reasons to use restrictive and non-restrictive clauses

You may wonder “why should I bother using restrictive and non-restrictive clauses?” Be assured that your writing will improve if you add these tools to your academic writing toolbox. Incorporating restrictive and non-restrictive clauses into your writing has two benefits: it helps 1) retain your readers’ attention and 2) improves flow and style.

A string of short, simple sentences impedes the readers’ attention. Their choppiness distracts the reader from the meaning of the text. They also increase reader fatigue. The result is your text is harder to understand.

Above is an example of a series of short, simple sentences. Each sentence either contains information that is necessary to the meaning I’m trying to convey or improves context.  Below is what it would look like with restrictive and non-restrictive clauses.

A string of short, simple sentences, which makes the text choppy, distracts the reader from the meaning of the text and impedes the readers’ attention. Distractions that increase reader inattention and fatigue make your text harder to understand.

Although there are only 4 sentences in the simple-sentence example, it feels harder to read. Restrictive and non-restrictive clauses in the second example improve style and flow, resulting in easier reading. Notice that the clauses don’t disrupt the flow of the sentence, but they combine information from two or more sentences into one sentence that is comprehensive.

Eureka!

Examples in science writing

Below are examples taken from my PhD thesis.

“The sensitivity of 18 and its derivatives to purification is a result of the electron density of the indole core, which increases the potential for heterolysis at C(1).”

Without the non-restrictive clause the text must be split into two sentences to convey the same information, resulting in a choppy construction.

“The sensitivity of 18 and its derivatives to purification is a result of the electron density of the indole core. It increases the potential for heterolysis at C(1).”

Here is an example with the restrictive clause. The restrictive clause provides the necessary information that only certain conditions were possible to explore.

“To further reduce the risk of C(10) heterolysis in the “real” system, conditions to remove the pyrrole carbinol that do not require an aqueous workup were investigated.”

“To further reduce the risk of C(10) heterolysis in the “real” system, conditions to remove the pyrrole carbinol were investigated.”

Without the restrictive clause, the meaning of the sentence is different. Key information is missing, which may mislead the reader.

Give it a try!

Writing is a skill that is learned through practice. When you edit your draft, try to use the restrictive and non-restrictive clauses to improve flow and reduce choppiness. Over time you’ll become proficient at using them to clearly convey your complex science.

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