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Subject Index - Grammar and Usage

a and an

Use "a" before any acronym or word that begins with a consonant sound. Use "an" before any acronym or word that begins with a vowel sound. An acronym is pronounced as a word (for example, a HEPA filter); an initialism is pronounced as its letters (for example, an NGO). The first sound of the word or letters indicates whether to use "a" or "an." Examples: a light-water reactor, an LWR; a Human Resources Office memo, an HRO memo; a nongovernmental organization, an NGO; a National Renewable Energy Laboratory subcontract, an NREL subcontract.

affect and effect

"Affect" is usually a verb, and "effect" is usually a noun.

affect (verb):

The new deposition process affected the efficiency of the device.

effect (noun):

We measured the effect of the new process on the efficiency of the device.

These words can be confusing because "affect" can sometimes be a noun (when it denotes an emotion), and "effect" can be a verb (when it means "to bring about").

assure, ensure, and insure

"Assure" means to make sure or give confidence. "Ensure" means to guarantee. "Insure" means to provide or obtain insurance.

The manufacturer assured the group the equipment would work properly.
Ensure the lid is fitted properly before starting the experiment.
The laboratory must insure the new equipment before it can be used.

because and since

"Because" indicates a cause-and-effect relationship. "Since" indicates a time relationship.

Because the equipment malfunctioned, the experiment failed.
Since we began using the new procedures, there have been no more malfunctions.


1. Proper Nouns

Capitalize proper names. These include the names of government programs, official projects, formal groups, organizations, companies, titles when they precede a name (use lowercase in titles that follow the name), specific geographic areas or features, and ethnic groups.

When referring to NREL, "National Renewable Energy Laboratory" is capitalized, but "the lab," "the laboratory," and "national laboratories" are not.

the Alcohol Fuels Program
the Ethanol Project
the Human Resources Office
the U.S. Bureau of Mines
Solarex Corp.
President Carter
Christine Johnson, president and chief executive officer
the Southwest
Lake Powell
the Colorado River
African, Asian, Black, Caucasian, Hispanic, or Native Americans

One exception to this rule is companies and products with stylized lowercase or "camel cap" names (e.g., eBay, iPhone). In these cases, use the company’s or product’s preferred capitalization.

2. Figure Captions, Table Titles, and Section Headings

Figure captions: Capitalize only the first word and proper nouns in figure captions. No period needed (unless there are multiple full sentences).

Figure 1. Results for the electrochromic window developed at NREL

Table titles and section headings: Capitalize the main words of table titles and headings and subheadings, including the second word in a hyphenated term (e.g., "PV Program Five-Year Plan"). No period needed.

Table 1. Number and Frequency of Defects in Six Samples

Testing the 7.6-m Blades
Results for E. Coli
Development of Method To Detect Anomalies

Do not capitalize:

  • Articles (e.g., "a," "an," and "the") unless they begin the title or heading
  • Conjunctions of three or fewer letters (e.g., "and," "or," "nor," "yet," "so," and "but")
  • Prepositions of three or fewer letters (e.g., "for," "of," "on," and "up").

Do capitalize:

  • Conjunctions (e.g., "than") and prepositions of four or more letters (e.g., “from,” “with,” “above,” “after,” “down,” “inside,” “over,” and “into”)
  • "To" as an infinitive (but lowercase as a preposition, e.g., “Scientists Travel to Chile To Engage Utilities”)
  • Verbs, including "is" and "are."

For journal/conference submissions or other non-NREL publications, follow the style recommended by the professional society or publisher.

3. Titles

Capitalize titles when they precede the person's name. Lowercase titles and names of groups when they follow the name.

Chief Operating Officer Mark Wilson
Mary Jones, the president of the company
John Smith, the chair of the committee

4. Trade Names

Capitalize trade or brand names, and include a trademark, copyright, or other symbol only when it's an Alliance-registered trademark. Include the symbol the first time you use the trade name in body text (not in a title, acronym list, or section header); thereafter, you may omit the symbol. Also use superscript for trademark symbols. See the trademark symbols entry for a list of Alliance trademarks.

5. Taxonomic Names

When writing about botanical and zoological divisions, capitalize the names of all divisions higher than species: genera, families, orders, classes, and phyla. Italicize genera, species, and varieties.

Clostridium thermocellum
Escherichia coli

After you first mention them (and spell them out), you can abbreviate most generic names followed by species names.

C. thermocellum
E. coli

See also captions, fiscal year, geographic regions, headings and subheadings, states and countries, and tables.

compose and comprise

"Composed of" is correct; "comprised of" is incorrect. See the examples below.

The United States is composed of 50 states.
The parts constitute the whole.
The whole comprises its parts.

The department comprises four groups; each group is composed of five to seven scientists, technicians, and support staff.

criterion, datum, memorandum, phenomenon, and their plurals

"Criterion" is a singular noun (one criterion), and "criteria" is the plural (two or more criteria). "Data" is the plural of "datum." The plural of "memorandum" can be either "memoranda" or "memorandums." "Phenomenon" is singular, and "phenomena" is plural.

first-person pronouns

See personal pronouns.

hyphens, compound words, and unit modifiers

Hyphenation rules can be intimidating, but remember that the ultimate goal is to provide as much clarity and consistency as possible. If you can’t find the proper hyphenation in this style guide, consult the AP Stylebook, followed by Merriam-Webster.

1. Verb Phrases: Verb, Noun, and Adjective Forms

Verb phrases that contain an adverb (e.g., build up, set up, start up, and break down) are usually written as two words. The noun and adjective forms of these words are usually one word, although there are exceptions.

We observed the slow buildup of biofouling on the blades.
The algae began to build up.

We helped with the setup.
To set up the experiment, begin with fresh samples.

The startup costs were more than we estimated.
The project is expected to start up next year

I think I'm having another breakdown.
It's time to break down the tent.

2. Compound Words Containing Prefixes and Suffixes

In most cases, you don't need a hyphen between prefixes or suffixes and the root words.


threefold, hundredfold
(also 100-fold)

Sometimes hyphens are needed when the root word begins with the same letter that the prefix ends in.


Use a hyphen between prefixes and proper nouns (but not common nouns) or dates whether they're used as nouns or modifiers.


Use two hyphens when adding a prefix to a word that already contains a prefix, even when there is no hyphen after the prefix in the original word.


Finally, these prefixes usually require a hyphen: "ex," "self," and "quasi."

3. Unit Modifiers With and Without Hyphens

Use a hyphen to indicate that words have been combined into a unit modifier, which is a descriptive expression composed of two or more words that form one new meaning. For example, in the term "flat-plate collector," "flat-plate" is the unit modifier. Here are some examples of unit modifiers that usually include hyphens:

low-level radiation
last-minute addition
high-temperature process
fatigue-induced wear
nine-story building
cost-effective solution

To see how adding the hyphen can prevent confusion, consider these examples:

The scientists tested a new defect causing gas.
The scientists tested a new defect-causing gas.

In the first example, the scientists might seem to have tested a defect; in the second example, it's clear that they tested a gas.

You don't need a hyphen in common unit modifiers that are not ambiguous or confusing.

high school students
solar radiation resource
solar thermal electric systems

Don't use a hyphen when both words of a unit modifier are capitalized.

Biofuels Program objectives
Pacific Ocean exploration
World Cup qualifier

Leave out the hyphens if you rewrite a sentence so the words in the unit modifier come after the noun they describe

We purchased state-of-the-art lab equipment.
We purchased lab equipment that reflects the state of the art.

They made some last-minute adjustments.
They made some adjustments at the last minute.

Don't use a hyphen with a unit modifier containing an adverb ending in "-ly."

heavily skewed results
frequently missed deadlines
commonly seen mistakes

When you use numbers in unit modifiers, retain all the necessary hyphens.

2-ft-diameter tubes
13-cm-wide substrate

Or rewrite the sentence to omit the hyphens.

tubes that are 2 ft in diameter
a substrate that is 13 cm wide

Use suspended hyphens when your compound modifier is interrupted by another word, such as part of a list.

light-, medium-, and heavy-duty vehicles
5- and 10-m blades

Suspended hyphens can also be used for different prefixes on the same root word (micro- and mesoscale), but the preferred style is to write out each word fully (microscale and mesoscale). Use your best judgment, considering both the context and audience.

4. Common Hyphenated Terms

Certain words and phrases are always hyphenated, regardless of context. Examples include:

decision-making (but decision maker)

it's and its

Even though "it's" has an apostrophe, it isn't a possessive pronoun. "It's" is a contraction, a short form of two words, like "isn't." "It's" always means "it is." "Its" is the possessive form of "it." Like "his," "hers," and "ours," the possessive "its" never needs an apostrophe.

It's a shame that the company lost its biggest investor.

misplaced modifiers

Modifiers in the wrong place can make a sentence confusing.

After identifying the correct material, the test procedure took about 5 minutes.

In this example, it isn't clear who or what identified the correct material. This might be better: After identifying the correct material, we conducted the 5-minute test procedure.

After being lost under a pile of old reports for 5 years, she finally found the manuscript.

What, or who, was lost—the manuscript, the woman, or the reader? Try to keep modifiers as close as possible to the people and things they describe. Strunk and White, authors of The Elements of Style, say this: "Modifiers should come, if possible, next to the word they modify." This is especially true for sentences containing introductory prepositional phrases or clauses followed by a comma.

nonrestrictive phrases and clauses

A nonrestrictive phrase or clause is one that adds information but is not essential to the meaning of the sentence.

The principal investigator, who has studied thin films for 10 years, will chair the panel discussion.

The passive solar features, which were suggested by NREL staff, reduced the agency's energy bills by 30%.

Nonrestrictive or nonessential phrases and clauses are enclosed between two commas when the phrase or clause is within a sentence, and they usually begin with "which" rather than "that." See also restrictive phrases and clauses and which and that.

noun and adjective strings

Try not to string too many nouns and adjectives together in a sentence. An "agency personnel communications interface display" could also be called a "display of the communications of the agency's personnel." Better yet, it could just be called the "staff bulletin board."


To give your writing more flow and vigor, try changing some of the nouns (especially those ending in -tion and -ment) to verbs (e.g., determine, complete, accomplish, achieve, measure, convert, characterize, combine) and other parts of speech. Doing this will move your readers along more quickly and make it easier for them to understand your text. In these examples, we changed some of the nouns in the first sentences to verbs and other parts of speech.

Contraction of the tree stems occurred with rapidity.
The tree stems contracted rapidly.

The frequent result of this process is the combination of the molecules.
This process frequently causes the molecules to combine.

The application of fertilizer has the result of stimulation of the yield.
Applying fertilizer stimulates the yield.

Which sentences were easiest to read and understand?

over and under

In cases involving quantity, use "more than" rather than "over," and use "fewer than" or "less than" rather than "under." In cases involving temperature, use "higher than" or "lower than" or "warmer than" or "cooler than." In cases involving weight, use "heavier than" or "lighter than."

More than 500 people attended the conference, about 100 fewer than last year.


Use parallel construction in sentences as well as in lists. Express all similar sentence elements (subjects, verbs, verbals, objects) in a similar way.

Not Parallel Structure:
The lever was moved completely forward, going slightly to the right, and then it went backward halfway in order to complete the procedure.

We are not only responsible to our chief customer but also the taxpayers.

Parallel Structure:
To complete the procedure, push the lever all the way forward, slide it slightly to the right, and then pull it halfway back.

We are responsible not only to our chief customer but also to the taxpayers.

personal pronouns

First-person pronouns may be used in technical communications when appropriate, and some scientific and technical associations (such as the American Institute of Physics) encourage technical writers to do so. Common first-person pronouns include "we," "our," and "us." Personal pronouns can prevent confusion by clearly and concisely showing who performed an experiment or procedure.

We tested several hundred isolates that were able to ferment glucose.

We deposited a thin film of doped cadmium on the substrate.

Which of the following two sentences is easier to read and understand quickly?

It was determined that the workshop was a success.

We agreed that the workshop was a success.

See also active voice and passive voice.


See hyphens, compound words, and unit modifiers and scientific notation.

principal and principle

"Principal" often means "chief" or "main," such as the principal investigator in a research project or the principal of a high school. "Principle" often refers to a belief, value, or rule.

race and ethnicity

As a laboratory that strives for diversity of perspectives and inclusivity, our word choices, style, and tone must be carefully considered, particularly when it comes to topics related to race and ethnicity.

Capitalize Black when referring to African Americans or, more broadly, in any racial, ethnic, or cultural sense; do not capitalize white. Do not use the terms “Black(s)” or “white(s)” as singular or stand-alone nouns referring to a person or people. In the plural form, “Black people,” “white people,” “Black scientists,” and “white scientists” are preferable when clearly relevant.

NREL's Black Employee Resource Group focuses on developing and supporting a vibrant community for NREL staff that identify as Black or of African descent.

Capitalize “Indigenous” in reference to original inhabitants of a place, aligning with long-standing capitalization of other racial and ethnic identifiers such as Latino, Asian American, and Native American. (Note that no hyphen is used in dual heritage terms such as “Asian American” and “Mexican American.”) Capitalize “Elder” when referring to a tribal or religious leader, but lowercase it when used to identify someone by age or when used generally.

The research team visited Indigenous communities throughout the Midwest to gather insights from local Elders.

The term “tribal” is lowercase when not part of an entity’s official name, and “tribe” is lowercase as a common noun, such as when generally referring to multiple distinct tribes. However, if the client or tribe feels strongly about capitalizing "tribe" or "tribal," we should honor their preference. Capitalize the words “tribe” and “nation” when part of a formal name.

the Kenaitze Indian Tribe
a citizen of the Navajo Nation
NREL researchers invited input from many tribal councils.

In Alaska, the Indigenous groups are collectively known as Alaska Natives. Both “American Indians” and “Native Americans” are acceptable terms when referring to two or more people of different tribal affiliations. “First Nation” is the preferred term for native tribes in Canada. “Indian” is used to describe the peoples and cultures of the South Asian nation of India and should not be used as shorthand for American Indians, unless that is how a particular group prefers to be referenced.

CCHRC staff worked with Alaska Natives and First Nation tribes to design specialized heating equipment.

For additional details, refer to the AP Stylebook's race-related coverage.

restrictive phrases and clauses

Do not use commas around restrictive phrases and clauses. They are essential to the meaning of the sentence, in contrast to nonrestrictive phrases and clauses, which simply add information that is not essential.

This is the house that Jack built.

See also which and that.


If you can't find a word or phrase in this style guide, consult the following reference guides in this order: (1) The Associated Press Stylebook and (2) Merriam-Webster's Collegiate Dictionary, Eleventh Edition.

For spelling out numbers, see numbers.

that and which

See which and that.


Use lowercase a.m. and p.m. (with periods) to denote "ante meridiem" and "post meridiem" (before and after noon). Use a colon to separate hours from minutes except for the top of the hour.

  • 11 a.m. (not 11:00 a.m.)
  • 3:30 p.m.

unit modifiers

See hyphens, compound words, and unit modifiers.

which and that

Standard American English uses "which" for nonrestrictive or nondefining phrases and clauses and "that" for restrictive or defining phrases and clauses. The word "which" usually signals the approach of added, nonessential information. When a phrase or clause is not essential to the meaning of a sentence, use the relative pronoun "which" and enclose the phrase or clause in commas. See also nonrestrictive phrases and clauses and restrictive phrases and clauses.

This paper, which she has been working on for three weeks, discusses string theory.

When a phrase or clause is essential to the meaning of a sentence (that is, the sentence would not make much sense without it), use "that" and leave out the commas.

The paper that he completed recently will be presented in New York; the paper that he finished last summer will be presented in Philadelphia.