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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.

 

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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All-Topics Index


The following index makes searching for a specific topic easier and links to the appropriate place in the sequenced material. We think we have most of them, but please email us at writingcenter@nps.edu if we are missing something!

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A

abbreviations

abstracts

academic writing

acronyms

active voice

apostrophes

argument

article usage

assignments, understanding them

audience

 

B

body paragraphs

brainstorming

building better sentences tips

 

C

citations

citation styles

clarity

clustering

coaching sessions, about

colons

commas, FANBOYS

commas, introductory

commas, list

commas, nonessential elements

commas, Oxford

commonly confused words 

compare-and-contrast papers 

concision

conclusions

conjunctive adverbs

coordinating conjunctions

copyright and fair use

critical thinking  

 

D

dangling modifiers

dashes

dependent marker words

double submission of coursework

drafting

 

E

edit your own work

editing – outside editors

exclamation points

executive summary

 

F

FANBOYS

FAQs

footnotes

free-writing

 

G

gerunds

grammar

group writing

 

H

hyphens

 

I

ibid.

introductions

 

J

Joining the Academic Conversation

 

L

LaTeX

library liaisons 

literature reviews 

logic and analysis 

 

M

memos

methodologies

 

N

note-taking

numbers

 

O

organization

outlining

Oxford comma

 

P

paragraph development 

parallelism

paraphrasing

parts of speech

passive voice

periods

persuasion

phrases and clauses

plagiarism, how to avoid through citations

plain language

polishing

prepositional phrases 

prepositions

pronouns

punctuation

purpose of research

 

Q

questions

quotation marks 

quoting

 

R

reading with intent

redundancies                                                                

reference software

reflection papers 

research

research questions

reverse outlining 

revising passive voice into active voice

revision

roadmaps                                            

run-on sentences 

 

S

self-citing

semi-colons

subjects, grammatical

significance

so-what?

spelling

standard essay structure

STEM/technical writing 

style

subject/verb agreement

 

T

technical writing

that vs. which

thesis writing

thesis advisors

thesis process overview

thesis process tips

thesis proposals – common elements                                                     

thesis statements

tone, professional

topic sentences 

transitions

types of papers

 

U

United States or U.S.?

 

V

verbs and verb tense

 

W

which vs. that

Why write?

writer’s block 

writing process