Commas with non-restrictive and restrictive modifiers
The following comma rules apply to all varieties of academic English because the omission or misuse of commas in these contexts can alter the meaning of a clause or sentence and lead to misunderstanding.
Because punctuation conventions vary greatly across languages, the use of commas with non-restrictive and restrictive modifiers can be particularly challenging for writers of English as a second language. It is therefore important to understand the distinction between different types of modifiers and the comma rules that govern their use.
Non-restrictive modifier
A non-restrictive modifier adds additional information that is not necessary to our understanding of the clause or sentence. If we remove the modifier, the basic meaning of the clause or sentence does not change, even though it becomes slightly less informative.
Non-restrictive modifiers often have the form of relative clauses. Relative clauses begin with a relative pronoun, such as which or who.
Non-restrictive modifiers can also be phrases (such as dated 1833, famous for his dramatic historical scenes, a prominent French 19th century artist in the examples below). In grammar, these phrases are often called non-restrictive appositives.
Non-restrictive modifiers are enclosed in commas to indicate that they provide additional information. The commas are obligatory because they have a clear purpose: omitting the commas will either result in an ill-formed sentence or create a change in meaning.
- The painting The Execution of Lady Jane Grey by Paul Delaroche, which is dated 1833, is one of the highlights of the National Gallery's collection.
- The painting The Execution of Lady Jane Grey by Paul Delaroche, who is known for his dramatic historical scenes, is one of the highlights of the National Gallery's collection.
- The painting The Execution of Lady Jane Grey by Paul Delaroche, famous for his dramatic historical scenes, is one of the highlights of the National Gallery's collection.
- The painting The Execution of Lady Jane Grey by Paul Delaroche, a prominent French 19th century artist, is one of the highlights of the National Gallery's collection.
- The painting by Paul Delaroche, which depicts the execution of Lady Jane Grey, is one of the National Gallery's highlights.
- The painting, which is dated 1833, is the original.
Comment: In all the above examples, the material inside of commas could be omitted without altering the main message:
- The painting The Execution of Lady Jane Grey by Paul Delaroche is one of the highlights of the National Gallery's collection.
- The painting by Paul Delaroche is one of the National Gallery's highlights.
- The painting is the original.
Restrictive modifier
A restrictive modifier limits or specifies the meaning of the word it modifies. In other words, it provides information that is necessary to identify the person, thing or idea being discussed.
If a restrictive modifier is omitted, it may no longer be possible to identify the correct person, thing, or idea. Restrictive modifiers are not enclosed in commas in English.
As the following examples show, non-restrictive and restrictive modifiers may sometimes appear identical in every respect except punctuation. The commas are the only feature that distinguishes the two modifiers and indicates the difference in meaning.
It is worth emphasising that relative clauses that begin with the relative pronoun that are always restrictive in English. This means that they should never be enclosed in commas.
THE EXPLANATIONS HERE NEED SOME REVISION AND THE NUMBER OF EXAMPLES CAN BE CUT DOWN - I TRIED TO CLARIFY BUT THAT DIDN'T WORK
- The painting by Paul Delaroche, which depicts the execution of Lady Jane Grey, is one of the National Gallery's highlights.
Non-restrictive modifier reading: The punctuation provides additional information about a painting whose identity is already clear.
- The painting by Paul Delaroche which depicts the execution of Lady Jane Grey is one of the National Gallery's highlights.
Restrictive modifier reading: The punctuation implies that more than one painting by Delaroche is relevant in the context. The information about the subject matter, the execution of Lady Jane Grey, is necessary to identify which of his paintings is referred to.
- The painting by Paul Delaroche that depicts the execution of Lady Jane Grey is one of the National Gallery's highlights.
Restrictive modifier reading: The punctuation implies that more than one painting by Delaroche is relevant in the context. The information about the subject matter, the execution of Lady Jane Grey, is necessary to identify which of his paintings is referred to.)
- The painting by Paul Delaroche is one of the National Gallery's highlights.
The punctuation implies that only one painting by Delaroche is relevant in the context and its identity is already clear.
- The painting, which is dated 1838, is a forgery.
Non-restrictive modifier reading: Punctuation provides additional information about a painting whose identity is already clear.
- The painting which is dated 1838 is a forgery.
Restrictive modifier reading implies that there is more than one relevant painting. The information about the date is necessary to identify which painting is referred to.
- The painting that is dated 1838 is a forgery.
Restrictive modifier reading implies that there is more than one relevant painting. The information about the date is necessary to identify which painting is referred to.)
- The painting is a forgery.
The sentence structure implies that only one painting is relevant in the context and its identity is already clear.
- The painting, displayed in an ornate gilded frame, is a forgery.
Non-restrictive modifier reading provides additional information about the painting being referred to.
- The painting displayed in an ornate gilded frame is a forgery.
Restrictive modifier reading implies that there is more than one relevant painting. The description of the frame is necessary to identify the one referred to.
- The painting that is displayed in an ornate gilded frame is a forgery.
Restrictive modifier reading implies that there is more than one relevant painting. The description of the frame is necessary to identify the one referred to.
- The painting is a forgery.
Sentence structure implies that only one painting is relevant in the context and its identity is already clear.
Separating non-restrictive and restrictive modifiers
One way to try to distinguish between non-restrictive and restrictive modifiers is to add the expression by the way. If by the way fits naturally into the context, the modifier is likely to be non-restrictive and the commas are therefore obligatory.
- The painting The Execution of Lady Jane Grey by Paul Delaroche, which by the way is dated 1833, is one of the highlights of the National Gallery's collection.
- The painting The Execution of Lady Jane Grey by Paul Delaroche, who by the way is known for his dramatic historical scenes, is one of the highlights of the National Gallery's collection.
- The painting by Paul Delaroche, which by the way depicts the execution of Lady Jane Grey, is one of the National Gallery's highlights.
By contrast, combining by the way with a restrictive modifier produces an unclear and unnatural reading. If this happens, the modifier should not be enclosed in commas.
- Those students who submit their assignments late will lose marks.
Restrictive modifier reading: only specific students, namely those who do not submit their assignments on time, will lose marks.
- Incorrect: Those students who by the way submit their assignments late will lose marks. (intended meaning becomes unclear.)