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NASA SP-7084

 

Grammar, Punctuation, and Capitalization


A Handbook for Technical Writers and Editors

 

Mary K. McCaskill
Langley Research Center
Hampton, Virginia

Chapter 1. Grammar

 

1.1. Grammar and Effective Writing

 

All writing begins with ideas that relate to one another. An author chooses words that express the ideas and chooses an arrangement of the words (syntax) that expresses the relationships between the ideas. Given this arrangement of words into phrases, clauses, and sentences, the author obeys grammar and punctuation rules to form a series of sentences that will impart the ideas.

English rules of grammar originated in antiquity, but over centuries have evolved according to usage and are still changing today. Thus, grammar rules may change and may be inconsistent, but usually have a functional basis. This functional attitude toward grammar, and punctuation, is described in Effective Revenue Writing 2 (Linton 1962). A rule of grammar or punctuation with a functional basis will not prevent effective statement of ideas, nor will following all the rules ensure effective writing.

Effective writing requires good syntax, that is, an effective arrangement of sentence elements. Obviously, an editor is responsible for ensuring that a consistent and correct set of grammar and punctuation rules have been applied to a report (a process often called copy editing). However, language and substantive edits, as defined by Van Buren and Buehler (1980), involve revision of sometimes perfectly grammatical sentences to improve effectiveness of sentence structure. This chapter discusses grammar, and the next chapter concerns sentence structure with emphasis on methods of revision.

According to Webster's Ninth New Collegiate Dictionary, grammar means "the study of the classes of words, their inflections [changes in form to distinguish case, gender, tense, etc.], and functions in a sentence." An abundance of good, detailed grammar, writing, and usage books are available. This chapter is not meant to be a definitive grammar reference. It is intended to address grammatical problems often encountered in technical documents and to indicate preference when grammar authorities do not agree. Please refer to the books cited in the References section and others to complement and clarify the discussions that follow.

 

1.2. Nouns

 

Nouns change form to indicate case and number. The number of a noun is usually not a problem (though the number of pronouns and verbs corresponding to the noun may be). The three possible cases are nominative, objective, and possessive. In English, nominative and objective case nouns have the same form.

 

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1.2.1. Possessive Case

At Langley, the preferred rules for forming possessives are as follows (G.P.O. 1984; and Rowland 1962):

• Form the possessive of a singular or plural noun not ending in s by adding 's.

• Form the possessive of a singular or plural noun ending in s by adding an apostrophe only:

 

Singular

Plural

 

man's

men's

horse's

horses'

Jones'

Joneses'

• Form the possessive of a compound noun by adding 's to the end of the compound:

sister-in-law's home
John Doe, Jr.'s report
patent counsel's decision 

• Indicate joint possession by adding 's to the last element of a series; indicate individual possession by adding 's to each element:

Wayne and Tom's office (one office)
editor's, proofreader's, and typist's tasks

Some authorities (for example, Skillin et al. 1974; and Bernstein 1981) partially disagree with the second rule above. They state that the possessive of a singular proper noun is formed by adding 's even when the noun ends in s (for example, Jones's); however, a triple sibilant is always avoided (for example, Jesus').

 

1.2.2. Possessive of Inanimate Objects

In the past, the possessive case ('s) was not acceptable for inanimate nouns. Instead the preposition of was preferred, that is, strength of the laminate rather than laminate's strength..

Exceptions to this rule were inanimate words representing a collection of animate beings (for example, company's profits, university's curriculum) and words expressing measure or time (for example, 2 hours' work). Current practice is to dispense with both the 's and the of (Skillin et al. 1974):

company profits
university curriculum
laminate strength
2 hours work

 

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In fact, the use of 's on an inanimate object is no longer taboo, particularly if the object has some lifelike qualities (Bernstein 1981):

computer program's name
Earth's rotation

Whether an 's can properly be added to an inanimate noun seems to be a matter of idiom. We would not say, for example,

systems' analyst
table's top

 

1.3. Pronouns

 

All pronouns must have an antecedent (the noun they replace) with which they agree in number, gender, and person. In addition, some pronouns change form to indicate nominative, objective, and possessive case (for example, he, him, his).

• An apostrophe is never used to form possessive case pronouns.

 

1.3.1. Antecedents

Most grammatical errors involving pronouns result from the lack of a clear antecedent. The following sentences suffer from this problem:

He foresaw aircraft applications and thus emphasized rectilinear motions.
This causes complicated integral equations for other types of motion.

The boundary condition becomes a source term, which permits use of the
Green function. 

Required surface pressures are obtained in several ways, for example,
from blade element theory or experimental measurements. Whatever the
technique, it is usually available.

In the first two sentences the pronouns this and which refer to the idea of the previous sentence or clause and do not have a noun antecedent. The Writer's Guide and Index to English (Ebbitt and Ebbitt 1978) states that this "broad reference" usage of pronouns is acceptable in "general" writing, but should be avoided in "formal" writing. The danger of broad reference is that the antecedent (whether a noun or a clause) may not be clear. In the second sentence above, which appears to refer to term. The following revisions would be preferable:

He foresaw aircraft applications and thus emphasized rectilinear motion.
This emphasis causes complicated integral equations for other types of
motion. 

Because the boundary condition becomes a source term, the Green
function can be used.

In the third sentence, it is much too distant from its antecedent, pressures. Because of this distance, the pronoun does not agree in number with its antecedent.

 

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Bernstein (1981) discusses ambiguous or nonexistent antecedents under "Pronouns" and under particular words, for example, "Each" and "None."

• Grammatical errors involving pronoun antecedents can be avoided very simply: check every pronoun for a clear, appropriate antecedent and then ensure agreement between antecedent and pronoun.

 

1.3.2. Personal Pronouns

First person pronouns

Tichy and Fourdrinier (1988) attribute the pervasiveness of passive voice in technical writing to evasion of first person pronouns (I, we). In the early 1900's, first person pronouns were banished from technical writing to obtain objectivity; however, Tichy and Fourdrinier effectively demonstrate that objectivity is not always attained. Writing authorities no longer forbid, and sometimes encourage, the use of first person pronouns (CBE 1978; AIP 1978; Houp and Pearsall 1984; and Mills and Walter 1978). Thus, we in technical documents cannot be condemned, particularly when the opinion of the author (and a research staff) is being expressed: 

We believe that this effect is due to nozzle aspect ratio.

This use of we, meaning "I and others," should be distinguished from the editorial we, meaning "you readers and I" (Ebbitt and Ebbitt 1982). In technical documents the editorial we is often used in mathematical presentations:

Now we define a recursive relation for the (k + l)th iteration:
P k + 1 = (XT / k Xk ) -1

Tichy and Fourdrinier (1988) recommend that the antecedent of we always be made clear. They also offer advice on when to use first person pronouns and when not to.

Gender

Third person singular pronouns change form to indicate gender (he, she). When the pronoun could refer to either sex or when the antecedent's sex is unknown, the masculine pronoun is grammatical. However, in recent years, objections have been raised to this grammatical rule.

• It is preferred practice to avoid the masculine pronoun when the antecedent may be feminine. Often the antecedent can be made plural:

 

Poor

An editor must have guidelines on which to base his
revisions.

Better

Editors must have guidelines on which to base their
revisions.

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Or the wording of the sentence can be changed:

 

Poor

The listener may not fully perceive the sound because
his ear has a critical summation time of 1 sec.

Better

The listener may not fully perceive the sound because
the human ear has a critical summation time of 1 sec.

 

1.3.3. Relative Pronouns

Relative pronouns function not only as pronouns but also as conjunctions. The relative pronoun replaces a noun in a dependent clause and connects the clause to the rest of the sentence.

Antecedents of relative pronouns

Who and whom refer to persons.

Which refers to things.

That refers to things and in rare instances may refer to persons.

Whose, the only possessive case relative pronoun, may refer to either persons or things according to Bernstein (1981). Other grammar authorities disagree and condemn the use of whose to refer to inanimate nouns. We prefer whose when of which would be awkward:

Awkward

A low-cost process has been developed for making alumina,
the limited availability and cost of which have previously
inhibited its widespread use.

Better

A low-cost process has been developed for making alumina,
whose limited availability and cost have previously inhibited
its widespread use.

Awkward

The attenuation is accompanied by an echo the amplitude
of which is above the background level and the position of
which is related to the depth of the region.

Better

The attenuation is accompanied by an echo whose amplitude
is above the background level and whose position is related
to the depth of the region.

Which versus that

Which is always used in a nonrestrictive relative clause (one that could be omitted without changing the meaning of the basic sentence):

The most common examples of panel methods are the aerodynamic codes of Hess and Smith (ref. 26), which were originally developed for nonlifting surfaces.

Which may also be used in a restrictive relative clause. Note that proper punctuation of restrictive and nonrestrictive clauses is vital: commas enclose nonrestrictive clauses, but never enclose restrictive clauses (see section 3.5.2).

 

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• That is preferred for restrictive (or defining) relative clauses (Bernstein 1981): 

The most common examples of panel methods are the aerodynamic codes that Hess and Smith (ref. 26) designed for nonlifting bodies.

There are three exceptions to the use of that to introduce a restrictive clause:

Which must be used after a preposition (Bernstein 1981):

The shading in figure 2 indicates elements in which fibers have failed.

Which is used after the demonstrative that (Bernstein 1981):

The most commonly used aerodynamic code is that which Hess and Smith (ref. 26) designed for nonlifting bodies.

Which sounds more natural when a clause or phrase intervenes between the relative pronoun and its antecedent (Fowler 1944):

 Finite bodies can undergo motions (such as spinning) which complicate the equations.

Omission of that

That can sometimes be omitted from restrictive relative clauses, but this omission is not recommended:

Correct

The model they analyzed is the most realistic one studied.

Better

The model that they analyzed is the most realistic one studied.

 

Who versus whom

Who (and its indefinite derivative whoever) is the only relative pronoun that changes form to indicate case (who, whom, whose). When a relative clause is inverted, we have difficulty determining whether the pronoun is in nominative case (who) or in objective case (whom). The easiest way to resolve such questions is to change the relative clause to an independent clause by substituting a third person personal pronoun for the relative pronoun. For example, in the questionable sentence

Information derived from this contract may be transmitted to those who the Defense Department has cleared to receive classified information.

change the relative clause to an independent clause:

The Defense Department has cleared them to receive classified information.

The sentence requires a third person pronoun in objective case (them), so the relative pronoun must also be in objective case (... those whom the Defense ... ).

 

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1.3.4. Demonstrative Pronouns

Demonstrative pronouns refer to something present or near (this, these) or to something more remote (that, those). Technical writing tends to exhibit two types of problems involving demonstrative pronouns: broad reference (see section 2.2.1) and incomplete comparison (see section 2.5.2).

Broad reference

The demonstrative this is often used to refer to the idea expressed in the previous sentence, a practice to be avoided in formal writing (Ebbitt and Ebbitt 1982). For example,

The entire noise prediction methodology for moving bodies becomes autonomous. This means that improved models can be incorporated simultaneously in pressure and noise calculations.

Most loads could be reduced 0.8 percent if voltage was more closely regulated. Nonessential loads such as payloads could take advantage of this, but essential loads could not.

This type of construction is sometimes vague and usually unnecessary. Often the demonstrative pronoun can be deleted:

The entire noise prediction methodology for moving bodies becomes autonomous. Thus, improved models can be incorporated simultaneously in pressure and noise calculations.

Or the antecedent can be clarified:

Most loads could be reduced 0.8 percent if voltage was more closely regulated. Nonessential loads such as payloads could take advantage of voltage regulation, but essential loads could not.

Incomplete comparison

Demonstrative pronouns can often be used to complete vague comparisons:

Poor

The errors in this prediction are greater than in table III.

Better

The errors in this prediction are greater than those in table III.

But make sure that the antecedent and meaning are clear:

Unclear

West's results were in better agreement with ours than those of Long et al.

Either

West's results were in better agreement with ours than those of Long et al.

Or

West's results were in better agreement with ours than with those of Long et al.

 

See section 2.5 for further discussion of comparisons.

 

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1.4. Verbs

 

Verbs, the only words that can express action, change form to indicate person, tense, mood, voice, and number.

 

1.4.1. Tense

Verbs change form to indicate tense, or time that an action or state of being takes place. English has six tenses: present, present perfect, past, past perfect, future, and future perfect. Each of the six tenses has a progressive form indicating a continuing action. (See Text 4 of Effective Revenue Writing 1, IRS 1962.) Writing authorities do not specify exactly which tenses should be used in a technical document, but they universally agree that shifts in tense should occur only when the time of the action changes. In other words, the point of view of a report with respect to tense must be consistent.

The relationship between point of view and verb tense can be understood in terms of the four elements of discourse (Buehler 1970):

The elements are quite often mixed. For example, in the Results and Discussion section, behavior of models or specimens (narration) might be discussed alang with presentation of results in tables and figures (description) and explanation of results (exposition). Narration is usually in past tense while description and exposition are usually in present tense. Consistency in tense does not mean that all sentences are in the same tense; it means that sentences expressing the same point of view (or element of discourse) are in the same tense. Avoid shifting back and forth between points of view by grouping material with a consistent viewpoint; but when the viewpoint does shift, shift the tense accordingly.

Tenses of independent clauses of report

There are no firm rules concerning tense of various sections in a report. However, if an author is inconsistent in tense, the following guidelines might be helpful to the editor:

 

• The Summary is usually in past tense.

• Past research (for example, in references) is usually described in past tense. 

• Permanent facilities are usually described in present tense.

• Experimental procedures and apparatus for a particular study are usually described in past tense.

 

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• Behavior of models, specimens, etc., during the study is usually expressed in past tense, and results presented in the report's illustrative material are expressed in present tense:

Typical fracture profiles are shown in figure 21. These profiles show that fracture mode changed with cyclic exposure. The specimens failed ...

As shown in figure 10, the autorotative rolling moment is a nonlinear function of roll rate, so that as spin rate increased, the propelling moments became equal.

• Explanation of why results occurred are in present tense:

The data failed to provide any reasonable estimates for Cnr. This failure can be attributed to the small excitation of yawing velocity.

• The Concluding Section is usually in past tense except that conclusions (that is, deductions thought to be universally true independent of the specific conditions of the investigation) should be in present tense.

• The Abstract is usually in present tense.

Sequence of tenses

The logical time relation between the various verbs and verbals in a sentence is expressed by shifts in the tense of these verbs and verbals. Sequence of tenses is a very complicated subject, which is discussed in almost every grammar and writing book. Only the basic guidelines are given here; for a more complete understanding, refer to such reference books.

• When the principal verb is in a present or future tense, subordinate verbs may be in any tense:

The data indicate that lift increases with angle of attack up to = 35°.

The data indicate that the specimen failed in a noncumulative mode.

The data indicate that propellers will have a place as a propulsive device of the future.

• When the principal verb is in a past tense, the subordinate verb must be in a past tense unless the subordinate clause expresses a universal truth or an action that is still continuing:

The data indicated that lift increased with angle of attack up to = 35°.

Previous studies had indicated that alumina is a suitable fiber for reinforcement.

• The present tense forms of verbals refer to action occurring at the same time as the main verb; the past tense or perfect tense forms of verbals refer

 

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to action occurring before the action of the main verb. This principle is most easily seen for participles:

Photographs indicating nearly laminar flow justified this assumption.

Photographs taken during an earlier test justified this assumption.

 

1.4.2. Mood

The three moods in English are indicative, imperative, and subjunctive. Almost all verbs in technical documents are indicative. Imperative mood is sometimes used in instructions or descriptions of procedures. Subjunctive mood is rarely used and seems to be disappearing from English usage. However, there are two situations when the subjunctive should be used (Bernstein 1981):

 

• Subjunctive mood is used to indicate a command, suggestion, recommendation, or requirement:

The console operator instructed that the preflight inspection be repeated.

The committee recommends that this research be continued.

• Subjunctive mood is used to indicate a condition contrary to fact or highly improbable:

If the integral were not singular, the question could be solved easily.

Up to now, all discontinuous fiber-reinforced composites have low ductility. If their ductility were improved, they would be highly attractive materials for aircraft applications.

The subjunctive should be used only when the author wishes to imply strong doubt. Notice the subtle change in attitude when the subjunctive is not used in the above example:

If their ductility was improved, they would be highly attractive materials for aircraft applications.

 

1.4.3. Voice

The voice of a verb indicates whether the subject is performing the action (active) or receiving the action (passive). Writing authorities overwhelmingly prefer active voice because it is direct, clear, and natural. Overuse of passive voice weakens style and obscures responsibility. This preference for active voice is not a condemnation of passive voice. Tichy and Fourdrinier (1988) list five situations when the passive voice is appropriate:

• When the actor is unimportant, not known, or not to be mentioned

• When the receiver of the action should be emphasized

• When the sentence is abrupt in active voice

• When variety is needed in an active voice passage

 

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• When a weak imperative is needed (for example, "The figures should be corrected quickly" )

 

The first two items justify much of the passive voice in technical documents. See section 2.2.2 for a discussion of revising passive voice sentences to make them active voice.

 

1.4.4. Verb Number

A verb must agree in number with its subject. This is a simple and absolute rule. However, verb-noun disagreements (in number) are common grammatical errors, sometimes caused by words intervening between the subject and verb and sometimes caused by difficulty in determining the number of the subject.

• Some nouns have confusing singular or plural forms, for example,

aeronautics, sing.

equipment, sing.

apparatus, sing.

hardware, sing.

apparatuses, pl.

phenomena, pl.

data, pl. 1

criteria, pl.

Consult the dictionary or a usage book when there is a question concerning the number of a particular noun.

Subjects joined by coordinate conjunctions

• Subjects joined by and, whether singular or plural, require a plural verb.

• Singular subjects joined by or or nor require a singular verb.

• When a singular subject and a plural subject are joined by or or nor, the verb agrees in number with the subject nearer to it.

• When subjects are joined by and/or, the number of the verb depends on the interpretation of and/or. Either a singular or plural verb can be justified. Bernstein ( 1981 ) considers and/or a "monstrosity" and recommends that it be avoided. Often either and or or alone is sufficient.

Subjects with intervening phrases

Phrases that intervene between the subject and verb do not affect number of the verb; it always agrees with the subject:

Damping ratio as well as frequency agrees with the experimental values.

This error plus any other systematic errors appears in the output of the instrument.

 


1 Authorities disagree on the number of the noun data. Bernstein (1981) takes the traditional view that it is a plural noun, but Tichy and Fourdrinier (1988), Ebbitt and Ebbitt (1982), and IRS (1962) consider it to be a collective noun either singular or plural depending on its meaning. We prefer that data be plural in Langley reports.

 

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Collective subjects 

A singular collective subject, which names a group of people or things, is treated as singular when the group is considered a unit or as plural when the members of the group are considered individually:

Langley's research staff is well-known for its achievements in aeronautics.

Langley's research staff do not all publish their results in report form.

• The number of such words as most, all, some, half, part, or percent is governed by the number of the noun in the phrase that follows, or that could follow, them:

Most of the measurements contain this error.

Most of the disagreement between the plots is attributed to this error.

Six percent of the chord has laminar flow.

Of the subjects tested, six percent rate all the noises acceptable.

• When a number is used with a plural noun to indicate a single measurement, a singular verb is required:

Twenty liters of fuel has passed through the combustion system.

When such a subject is thought of as individual parts, a plural verb is appropriate:

Twenty milliliters of water were added, one at a time, to the solution.

 

Compound clauses with auxiliary verbs omitted

In compound sentences with passive voice verbs, the auxiliary verbs are sometimes erroneously omitted:

The wing plate was fabricated from nickel 201, its surface polished, and nickel rods welded to its edge.

• The omission of auxiliary verbs is grammatical unless the subjects change number (Rowland 1962). The above sentence should be

The wing plate was fabricated from nickel 201, its surface polished, and nickel rods were welded to its edge.

 

1.5. Adjectives

 

Since modifiers make up the bulk of most writing, their placement is very important to sentence structure.

In contrast to adverbs, adjectives are naturally placed near the noun or pronoun that they modify. Single-word adjectives and unit modifiers precede the noun and adjective phrases and clauses follow it. See section 2.2.3 for a discussion of placement of modifiers.

See section 2.5.1 for discussion of the degree (positive, comparative, and superlative) of adjectives.

 

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1.5.1. Articles

Indefinite articles a and an

• The indefinite article a precedes a word beginning with a sounded consonant, and an precedes a word beginning with a vowel sound.

• Whether a or an should precede an abbreviation or acronym depends not on its initial letter but on how the author expects it to be read (Bernstein 1981). For example, most people read "M.A." as letters rather than as "Masters of Arts," so "an M.A. degree" is appropriate. Likewise, we prefer "an NACA airfoil." However, "NASA" is not usually read as letters, so we prefer "a NASA airfoil."

Articles with coordinate adjectives

Whether or not articles are repeated before coordinate adjectives affects meaning (Rowland 1962).

• If coordinate adjectives each refer to different things or persons, articles are repeated when the modified noun is singular and are not repeated when the modified noun is plural:

Wrong

The transverse and shear strain is calculated for each specimen. (two strains)

Correct

The transverse and the shear strain is calculated for each specimen.

Or

The transverse and shear strains are calculated for each specimen.

• If coordinate adjectives refer to one thing or person, the article is not repeated:

Wrong

A more nonlinear and a lower stress-strain curve resulted from the test. (one curve)

Correct

A more nonlinear and lower stress-strain curve resulted from the test.

Omission of articles

There is a trend in modern writing, particularly journalism, to omit articles. Langley has traditionally preferred this "elliptical style" for symbol lists, figure captions, headings, and titles:

 

u ratio of [the] wing mass to [the] mass of air in [a] truncated cylindrical cone enclosing [the] wing

Figure 1. Effect of leak area on pressures, heating rates, and temperatures in [the] cove and at [the] bulkhead.

Spectral Broadening by [a] Turbulent Shear Layer

Bernstein (1981) calls elliptical style a "disfigurement of the language." The author, or editor, may prefer to retain (or restore) articles in symbol lists, figure captions, headings, and titles.

 

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1.5.2. Unit Modifiers

Technical writing abounds with unit modifiers, that is, combinations of words that modify another word:

The annular suspension and pointing system for space experiments is described.

These values identify the beginning of shock wave boundary layer interaction.

Separated flow wing heating rate values increase sharply toward a constant value.

Authors and editors often have difficulty deciding when and how to hyphenate these modifiers. Bernstein (1981) considers hyphens a necessary evil to be used only to avoid ambiguity. Certainly, unit mod)fiers need not always be hyphenated and hyphenation does not always prevent ambiguity.

Before agonizing over hyphenation of these modifiers, consider changing them to prepositional phrases to clarify their meaning. Perhaps this change only a few times in a report is sufficient to clarify the unit modifier when it appears subsequently.

Surely the prepositional phrases in the following sentences are clearer than the hyphenated unit modifiers:

Unit
modifier

The annular suspension-and-pointing system for space experiments is described.

Prep.
phrase

The annular system for suspension and pointing of space experiments is described.

Unit
modifier

These values identify the beginning of shock-wave-boundary-layer interaction.

Prep.
phrase

These values identify the beginning of interaction between the shock wave and boundary layer.

Unit
modifier

Separated-flow wing heating-rate values increase sharply toward a constant value.

Prep.
phrase

Heating rates on the wing over which the flow is separated increase sharply toward a constant value.

Too many prepositional phrases can make the sentence awkward and hard to read, as in the last example. The following might be preferable:

Separated-flow heating rates on the wing increase sharply toward a constant value.

Probably the best authority on hyphenation of unit modifiers is the G.P.O. (1984). Unfortunately we sometimes forget rule 6.16:

Where meaning is clear and readability is not aided, it is not necessary to use a hyphen to form a temporary or made compound. Restraint

 

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should be exercised in forming unnecessary combinations of words used in normal sequence.

• A unit modifier should not be hyphenated

• A unit modifier should always be hyphenated

Of course, there are many instances other than those listed above when a unit modifier may be hyphenated. See Skillin et al. (1974) and G.P.O.

 

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(1984) for discussions of permissible temporary compound words. The above guidelines are based on the hyphenation rules proposed by Murdock (1982). She attempted to eliminate the need for subjective decisions concerning the clarity of unit modifiers. Unfortunately, her rules do not always ensure clarity. It seems that authors and editors must subjectively decide whether or not a unit modifier is clear and readable without a hyphen.

 

1.6. Adverbs

 

Adverbs modify verbs, adjectives, and even other adverbs, but not nouns or pronouns. Adjectives can modify only nouns and pronouns. Grammatical errors sometimes occur when an adjective tries to modify a verb:

Wrong

The balance was mounted internal to the model.

Correct

The balance was internally mounted on the model.

Or

The balance was mounted inside the model.

Note the position of the adverb internally in the above example. The natural place for a single-word adverb is within the verb phrase. However, some adverbs can be moved within a sentence to change emphasis (see section 2.6). Although adverbial words and phrases can be moved easily within a sentence, they can be misplaced when their modification is not clear.

See section 2.5.1 for discussion of degree (positive, comparative, and superlative) of adverbs.

 

1.6.1. Misplaced Adverbs

Some adverbs such as only, almost, nearly, also, quite, merely, and actually must be placed as close as possible to the words that they modify (see the discussion of "only" in Bernstein 1981):

Misplaced

The approximation is only valid for u = 0.

Correct

The approximation is valid only for u = 0.

Misplaced

The flow had separated nearly over the whole wing.

Correct

The flow had separated over nearly the whole wing.

Misplaced

It is only necessary to apply equations (6) to (12) to compute D.

Correct

It is necessary to apply only equations (6) to (12) to compute D.

 

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1.6.2. Squinting Adverbs

An adverb "squints" when it is not clear whether it modifies the preceding or the following words:

Squinting

Although the operator eventually replaced the thermocouple, during that test, the temperature measurements were inconsistent.

Either

Although during that test, the operator eventually replaced the thermocouple, the temperature measurements were inconsistent.

Or

Although the operator eventually replaced the thermocouple, the temperature measurements were inconsistent during that test.

 

1.6.3. Split Infinitives

Despite the fact that split infinitives have usually been proscribed in formal writing, most, if not all, grammar authorities recommend splitting an infinitive to avoid ambiguity or awkwardness. In particular, do not place an adverb before or after an infinitive if in that position the adverb might appear to modify a word other than the infinitive:

Split

He agreed to immediately recalibrate the surface pressure instrumentation on the wing.

Squinting

He agreed immediately to recalibrate the surface pressure instrumentation on the wing.

Awkward

He agreed to recalibrate immediately the surface pressure instrumentation on the wing.

Split

The flow at = 0° was the first to completely establish itself over the wing.

Awkward

The flow at = 0° was the first completely to establish itself over the wing.

Squinting

The flow at = 0° was the first to establish itself completely over the wing.

• Avoid splitting an infinitive with a phrasal adverb. Such split infinitives are usually awkward.

 

1.7. Prepositions

 

Prepositions are handy little words that connect a phrase to a sentence and at the same time impart meaning. Prepositional phrases can function as adjectives, adverbs, or nouns.

When prepositions are used redundantly or unnecessarily, they should be deleted for the sake of brevity (see section 2.4.1).

 

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1.7.1. Prepositional Idioms

Choosing the right preposition to use in a particular construction is a matter of idiomatic usage, not governed by grammatical rules. Therefore, when questions arise concerning prepositional idioms, consult the dictionary, a usage reference (such as Bernstein 1981), or a list of such idioms (Skillin et al. 1974 and Rowland 1962 contain sections entitled "The Right Preposition" ). Some examples of prepositional idioms follow:

analogous to

correlation with

attempt (n.) at

implicit in

attempt (v.) to

similar to

coincident with

theorize about

different from

variance with

 

1.7.2. Terminal Prepositions

Most authorities agree that ending a sentence with a preposition is grammatical, although they often recommend avoiding terminal prepositions because sentences should end with strong words rather than weak ones (see section 2.6 for positions of emphasis in a sentence). If deleting a terminal preposition results in an awkward sentence or changes emphasis in the sentence, nothing has been gained:

Term. prep.

This hypothesis is intuitively difficult to disagree with.

Awkward

This is an intuitively difficult hypothesis with which to disagree.

Change emphasis

To disagree with this hypothesis is intuitively difficult.

Bernstein (1981) provides an excellent discussion of this topic. He summarizes by stating, "If by trying to avoid ending a sentence with a preposition you have seemed to twist words out of their normal order and have created a pompous-sounding locution, abandon the effort."

 

1.7.3. Repeating Prepositions

Prepositions must be repeated in coordinate phrases only when they are required for clarity or when their omission breaks rules of parallelism:

Unclear

Shock tests were conducted in nitrogen and oxygen.

Either

Shock tests were conducted in nitrogen and in oxygen.

Or

Shock tests were conducted in a mixture of oxygen and nitrogen.

Not parallel

Tests were conducted not only in nitrogen but also oxygen.

Correct

Test were conducted not only in nitrogen but also in oxygen.

Of course, prepositions (and articles) can be repeated for emphasis.

 

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1.8. Conjunctions

 

Conjunctions are classified as coordinating, joining sentence elements of equal grammatical rank, and as subordinating, joining elements of unequal rank.

 

1.8.1. Coordinating Conjunctions

Coordinating conjunctions join grammatically equal sentence elements; that is, they join a word to a word, a phrase to a phrase, or a clause to a clause. They thus provide important opportunities to use parallelism. See section 2.3 for a discussion of parallel construction. The three types of coordinating conjunctions are:

Coordinate conjunctions: and, but, or, nor

Correlative conjunctions: either ... or, both ... and, not only ... but also

Conjunctive adverbs: therefore, however, thus, hence, otherwise

Coordinate conjunctions

Coordinate conjunctions can join words, phrases, and clauses. The elements that they join must be equal grammatically. A coordinate conjunction cannot join a noun and prepositional phrase, for example:

Wrong

Pressures at the bulkhead, the seal, and in the cove are shown.

Correct

Pressures at the bulkhead, at the seal, and in the cove are shown.

Nor can a coordinate conjunction join a noun and a clause:

Wrong

Notable characteristics of the air duct system are the acoustic treatment of the ducts and that the compressor can force flow both ways through the system.

Correct

Notable characteristics of the air duct system are the acoustic treatment of the ducts and the ability of the compressor to force flow both ways through the system.

Correlative conjunctions

Correlative conjunctions are pairs of words that connect parallel sentence elements.

• Each member of the correlative must be followed by the same part of speech

Wrong

The microprocessor provides both radiometer control functions and formats the data.

Correct

The microporcessor both controls the radiometer and formats the data.

 

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Also it is good practice to keep elements joined by correlatives strictly parallel:

Poor

The subsystem not only measures temperature but it also provides real-time displays.

Better

The subsystem not only measures temperature but also provides real-time displays.

Poor

This duct serves either as an eductor that provides an exit to the atmosphere or as an inductor sucking air into the system.

Better

This duct serves either as an eductor exiting air to the atmosphere or as an inductor sucking air into the system.

Conjunctive adverbs

Conjunctive adverbs can be used to join independent clauses only. In contrast to coordinate conjunctions, conjunctive adverbs have more modifying character and less connective force.

 

• Clauses joined by conjunctive adverbs must be separated by a semicolon (or a period):

Coord. conj.

The differences were generally about 11 percent, but larger differences occurred at = 15°.

Conj. adv.

The differences were generally about 11 percent; however, larger differences occurred at = 15°.

 

1.8.2. Subordinating Conjunctions

Subordinating conjunctions connect dependent clauses to independent clauses. They are discussed in three categories:

Adverbial conjunctions, which join adverbial clauses to independent clauses: for example, because, though, after, where, so that.

Relative pronouns, which are discussed in section 1.3.3.

That, which is used as a function word to introduce dependent clauses.

Adverbial conjunctions

Subordinating conjunctions that join adverbial clauses to independent clauses are called adverbial conjunctions. The biggest problem with these conjunctions is deciding whether the dependent clause is restrictive or not in order that the sentence can be properly punctuated (see section 3.5.2).

Some of these conjunctions are often used improperly:

As, since, and while have meanings other than those involving time, so that care must be taken to ensure that their meaning is clear.

 

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If introduces clauses indicating condition; whether introduces clauses indicating alternatives:

Wrong

Aerodynamic forces were studied on a two-dimensional wing section to determine if similar trends would be calculated.

Correct

Aerodynamic forces were studied on a two-dimensional wing section to determine whether similar trends would be calculated.

Where refers to place or location. It is often used incorrectly to replace that, when, or a relative pronoun:

Wrong

This formulation is equivalent to the Prandtl-Glauert transformation, where the body is stretched to correct for the actual distance.

Correct

This formulation is equivalent to the Prandtl-Glauert transformation, by which the body is stretched to correct for the actual distance.

 

While used in the sense of although or whereas is becoming accepted, with reservation. Skillin et al. (1974) approve of using while to mean although so long as its use "does not defy the sense of at the same time." Bernstein (1981) describes this usage of while as acceptable, "but with less universal sanction."

For a better understanding of these or other usage problems, consult Bernstein (1981) or other usage references.

The subordinating conjunction that

The subordinating conjunction that is defined in the dictionary as a function word that introduces several types of dependent clauses, for example, noun clauses:

That the seven-term function does not result in a good approximation is apparent.

That may sometimes be omitted in noun clauses (particularly following such verbs as say, think, and believe), but this omission is not recommended:

Correct

The listeners believe the noise might hurt them.

Better

The listeners believe that the noise might hurt them.

Correct

The computation is adequate provided it is converged with respect to collocation order.

Better

The computation is adequate provided that it is converged with respect to collocation order.

 

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• When a phrase or clause intervenes between that and the rest of the dependent clause, that is sometimes incorrectly repeated:

Wrong

He concluded that because checks were made with 128 collocation points and only small differences were found, that the results shown were converged.

Either

He concluded that because checks were made with 128 collocation points and only small differences were found, the results shown were converged.

Or

Because he made checks with 128 collocation points and found only small differences, he concluded that the results shown were converged.

 

1.9. Verbals

 

The three types of verbals are the gerund (verb ending in ing used as a noun), the participle (verb used as an adjective), and the infinitive (verb preceded by to used as an adverb, adjective, or noun).

 

1.9.1. Coordinate Gerunds and Infinitives

Grammar authorities all remind us that a gerund takes a singular verb:

Substituting the expression into equation (2) yields ...

But these authorities are silent on the number of a verb following coordinate gerund subjects:

Substituting this expression in equation (2) and simplifying the result yields . . .

• We prefer a singular verb if a series of actions expressed by coordinate gerunds can be considered a single process.

• Likewise, the prepositions should not be repeated before coordinate gerunds or infinitives that express a process (Rowland 1962):

The following expression results from substituting equation (1) into equation (2), integrating by parts, and taking the limit.

The test procedure was to combine the samples in a large vat, stir the mixture, and then withdraw samples for analysis.

See section 1.7.3 concerning repetition of prepositions in coordinate phrases.

 

1.9.2. Idiom Requiring Gerund or Infinitive

Whether a particular verb should be followed by an infinitive or a gerund phrase is a matter of idiom, for example,

Correct

The display helped the pilot to cope with the increased work load.

Wrong

The display aided the pilot to cope with the increased work load.

 

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Although the meaning of these two sentences is the same, changing the verb changes the verbal required by idiom:

Correct

The display aided the pilot in coping with the increased work load.

Consult a usage reference (for example, Skillin et al. 1974) to check for these idioms; the

dictionary also offers an indication of idiomatic usage.

 

1.9.3. Dangling Verbals

An infinitive, gerund, or participle dangles when the agent of the action that it expresses is not clear.

Some authorities (IRS 1962; Tichy and Fourdrinier 1988) consider an introductory gerund or infinitive phrase to dangle when it does not modify the subject:

When using a nonaligning pitot static tube, the total velocity component cannot be exactly measured because of the swirl component.

To predict the thrust and power coefficients of the propeller, the aerodynamic coefficients must be provided.

Rowland (1962) considers such gerund phrases acceptable because "they are employed so frequently in technical writing that they may be said to be idiomatic." The same can be said of introductory infinitive phrases. These introductory phrases are clearly adverbial because no one would attribute their action to the subject. Note that the verbs in the above sentences are in passive voice, so that an unknown agent can be supplied for the verbals' actions. When the verb is in active voice, the verbal tends to dangle:

When using a nonaligning pitot probe, the swirl component precludes exact measurement of total velocity.

• Introductory gerund and infinitive phrases do dangle when they modify a noun in the sentence other than the subject:

Wrong

When using a nonaligning pitot static tube, total velocity cannot be measured exactly by the investigator because of the swirl component.

Correct

When using a nonaligning pitot static tube, the investigator cannot exactly measure total velocity because of the swirl component.

Although Rowland justifies introductory adverbial gerund and infinitive phrases because they are idiomatic and clearly adverbial, he does not extend this argument to participles. He condemns dangling participles as "slovenly English" and "weak constructions that should be replaced by more robust phrasing." Are dangling participles slovenly English? Or, like the dangling gerund, are they becoming idiomatic?

 

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Absolute participles

A class of apparently dangling participial phrases that have become idiomatic are absolute participles (Bernstein 1981). They have no antecedent and none is intended; that is, they are indefinite, for example,

The density mode is preferred provided that optical properties are measured.

Given a variable factor, the fluctuating flow components can be calculated from equations (31) to (38).

Either the density mode or the pressure mode can be used, depending on whether supporting optical measurements or probe measurements are made.

Other idiomatic absolute participles are

generally speaking

concerning

considering

regarding

judging

beginning

Such constructions must be truly absolute, with no antecedent in the sentence. In the following sentence, what appears to be an absolute participle is actually dangling:

Dang. partic.

An arbitrary factor controls the accuracy of the calculation depending on pressure fluctuations.

Better

A variable factor depending on pressure fluctuations controls the accuracy of the calculation.

Technical writing often contains absolute participles that are not idiomatic, for example,

The arbitrary factor can be assumed to be small and therefore can be neglected, yielding a first-order solution.

Such a participle might be justified by arguing that it is an absolute adjective construction modifying the whole sentence. However these participles can sometimes be made adverbial:

The arbitrary factor can be assumed to be small and therefore can be neglected to yield a first-order solution.

Sometimes a participle at the end of a sentence is not absolute, but actually modifies the subject in a nonrestrictive way:

Nonrestrictive partic.

Increasing the leak area caused the boundary layer to attach, thus decreasing heat transferred to the cove interior.

 

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The MLA's Line by Line (Cook 1985) does not object to such placement of a participle. However, these participles can usually be changed to a compound predicate:

Compound predicate

Increasing the leak area caused the boundary layer to attach and thus decreased heat transferred to the cove interior.

Do not confuse absolute participles with nominative absolute constructions, which are perfectly grammatical. Nominative absolutes have their own subjects and modify the whole sentence:

Dang. partic.

Maraging steels are promising for cryogenic service, having hardness at -320°F of 38Rc.

Nom. abs.

Maraging steels are promising for cryogenic service, their hardness at -320°F being 38Rc.

Adverbial participles

What appears to be a dangling participle is left when the preposition by is dropped from an adverbial gerund phrase. These "adverbial participles" may appear after the verb or at the beginning of the sentence:

Adverb. partic.

The logarithmic derivative is obtained using this least squares representation.

Gerund phrase

The logarithmic derivative is obtained by using this least squares representation.

Adverb. partic.

Neglecting the dependence of n on Reynolds number, the results of figure 11 can be used to estimate n.

Gerund phrase

By neglecting the dependence of n on Reynolds number, the results of figure 11 can be used to estimate n.

Adverb. partic.

Substituting equation (34) instead of equation (14), the terms for the fluctuating modes can be rewritten.

Gerund phrase

By substituting equation (34) instead of equation (14), the terms for the fluctuating modes can be rewritten.

Restoring by to these phrases adds very little to the above sentences. The participles in these sentences clearly modify the verbs; thus their meaning is clear. But participles are, by definition, adjectives, so that adverbial participles are not grammatical. Also there are methods of revising adverbial participles other than restoring their by. In the following sentences, stronger constructions replace the participial phrases:

Prep. phrase

The logarithmic derivative is obtained from this least squares representation.

 

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Prep. phrase

With the dependence of n on Reynolds number neglected, the results of figure 11 can be used to estimate n.

Gerund subject

Substituting equation (34) instead of equation (15) allows the terms for the fluctuating modes to be rewritten.

Dangling participles

When a participle genuinely appears to modify the wrong noun, truly dangling and thus much more offensive:

Dang. partic.

Using a nonaligning pitot probe, the swirl cormponent precludes exact measurement of total velocity.

Better

When a nonaligning pitot tube is used, the swirl component precludes exact measurement of total velocity.

Dang. partic.

The shock is essentially normal near the body, producing subsonic flow.

Better

Near the body is an essentially normal shock producing subsonic flow.

Dang. partic.

Encouraged by these results, a new research effort was begun.

Better

Encouraged by these results, we began a new research effort.

Recommendations

• When an introductory gerund or infinitive phrase is clearly adverbial, we consider its use idiomatic and therefore we do not consider it dangling.

Although no writing authorities now claim that adverbial participles and nonidiomatic absolute participles are becoming acceptable in technical writing, such participles are widely used and well understood. Forbidding their use is perhaps like forbidding the tide to rise. These participial constructions are certainly not grammatical, but they are rarely misunderstood.

• So long as an adverbial or absolute participle does not appear to modify the wrong noun, it is acceptable, but not encouraged.

 

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