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Commas, Nonessential Elements


You might be asking yourself why commas would delineate “nonessential elements” at all: doesn’t concision call for removing whatever is unnecessary?

It does. But “nonessential” in this case does not refer to information that is extraneous to your meaning; rather, it refers to supplementary (or “nonrestrictive”) information about something—as opposed to information that specifies a subset or item, known as “essential” or “restrictive” information. One of the comma’s jobs is to distinguish between these types of information.

The idea is harder to describe than to illustrate. Perhaps the most familiar manifestation of the essential–nonessential distinction is the choice between that and which.

Essential Tools: “That” vs. “Which” and “Who” vs. “, Who”

Simply put, that indicates essential (specifying) information, while which—preceded by a comma—indicates nonessential (supplementary) information:

  1. “The rebel groups that banded together” = not all of the rebel groups banded together; right now, we’re only talking about those that did
  2. “The rebel groups, which banded together” = all of the rebel groups in fact banded together; we’re talking about all of them

This same consideration determines whether or not to put a comma before who:

  1. “The rebels who banded together” = not all of the rebels banded together; right now, we’re only talking about those who did
  2. “The rebels, who banded together” = all of the rebels in fact banded together; we’re talking about all of them

Note that the essential vs. nonessential distinction does not play a role in selecting "who" vs. "whom" (both of which can introduce restrictive or nonrestrictive information).

Elided “That” and “Which”

We frequently encounter constructions that do not actually contain “that” or “which” but that are nevertheless able to maintain the distinction between essential and nonessential information by including or omitting commas. Take this example:

  1. The peace treaty, signed by all the belligerents, lasted for more than 400 years.
  2. The peace treaty signed by all the belligerents lasted for more than 400 years.

Version 1 contains an implicit “which”:          

The peace treaty, [which was] signed by all the belligerents, lasted for more than 400 years.

Even without the “which,” the commas indicate that this sentence is about one particular peace treaty that, it just so happens, was signed by all the belligerents. Placed between commas, the information about the signatories is nonessential or nonrestrictive—not because it’s superfluous to the discussion (it might or might not be) but because it’s not there to help us differentiate this treaty from any other; it’s just additional information about the only treaty this sentence could be talking about.

Version 2 contains an implicit “that”:

The peace treaty [that was] signed by all the belligerents lasted for more than 400 years.

With or without “that,” the absence of commas here indicates that this same information is now essential insofar as it specifies the treaty in question, distinguishing it from other treaties. That is, the information about the signatories restricts the statement about how long the treaty lasted to only that treaty signed by all the belligerents; this statement does not apply to any of the other treaties this sentence could otherwise have been talking about.

We might expect such a piece of information to be followed by a contrasting one:

The peace treaty signed by all the belligerents lasted for more than 400 years; those treaties signed by only some of the belligerents fell apart much more quickly.

Nonessential Elements Commas Links

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Writing Topics A–Z


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A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q R  S  T  U  V  W  X  Y  Z

A

abbreviations

abstracts

academic writing

acronyms

active voice

adjectives, compound

advisor, selecting and working with

AI

apostrophes

appointment with GWC coaches, how to schedule

argument

article usage

artificial intelligence

assignments, understanding them

audience

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B

body paragraphs

booking an appointment with a GWC coach

brackets, square

brainstorming

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C

capitalization

citations

charts

ChatGPT

citation software

citation styles

clauses

clarity

clustering

coaching, about

coaching, how to schedule

colons

comma splices

commas, FANBOYS

commas, introductory

commas, list

commas, nonessential / nonrestrictive information

commas, Oxford

commas, serial

common knowledge

commonly confused words

compare-and-contrast papers

compound adjectives / modifiers

concision

conclusions

conference presentations

conjunctive adverbs

coordinating conjunctions

copyright and fair use

critical thinking

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D

dangling modifiers

dashes

dependent clauses

dependent marker words

display equations

distance learning

double submission of coursework

drafting

Dudley Knox Library

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E

editing your own work

editing: outside editors

em dash

en dash

equations

exclamation points

executive summary

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F

FANBOYS

FAQs

figures

first person, use of in academic writing

footnotes

fragments

free-writing

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G

generative artificial intelligence (AI)

gerunds

grammar

graphics

graphs

group writing

GWC appointment, how to schedule

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H

homophones

Honor Code, NPS

human subjects research

hyphens

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I

ibid.

incomplete sentences

independent clauses

Institutional Review Board

interviews, conducting

introductions

IRB

iThenticate

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J

Joining the Academic Conversation

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L

LaTeX

library liaisons

lists, syntax of

literature reviews

logic and analysis

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M

M dash

making a GWC appointment

mathematics

memos

methodology

modifiers, compound

modifiers, misplaced

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N

N dash

nominalizations

note-taking

noun clusters

numbers

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O

organization

outlining

Oxford comma

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P

paragraph development

parallelism

paraphrasing

parentheses

parts of speech

passive voice

periods

persuasion

phrases vs. clauses

plagiarism, how to avoid

plagiarism-detection software

plain language

polishing

prepositional phrases

prepositions

pronouns, clarity with

pronouns, grammar of

proofreading

publishing

punctuation

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Q

questionnaires, administering

questions

quotation marks

quoting

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R

Reading with Intent I

Reading with Intent II

redundancies

reference software

reflection papers

research

research guides, discipline-specific

research questions

restrictive vs. nonrestrictive information

reusing papers

reverse outlining

revision

roadmaps

run-on sentences

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S

scheduling a GWC appointment

self-citing

semicolons

sentence fragments

serial comma

signal phrases

significance

so what?

source blending

sources, engaging with / critiquing

sources, evaluating the reliability of

sources, citing

spelling

standard essay structure

STEM / technical writing

Strategic Reading I

Strategic Reading II

style

subject–verb agreement

subjects, grammatical

subordinating conjunctions

summarizing

surveys, administering

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T

tables

teams, writing in

technical writing

tense

that vs. which

thesis advisor, selecting and working with

thesis process overview

Thesis Processing Office (TPO)

thesis proposals: common elements

thesis statements

thesis writing

this, that, these, those

tone, professional

topic sentences

transitions

types of papers

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U

United States or U.S.?

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V

verbs and verb tense

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W

which vs. that

why write?

writer’s block

writing in groups / teams

writing process

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Z

Zotero

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