Chapter 2. Sentence Structure

2.1. Sentence Structure and Effective writing

Effective writing involves far more than following rules of grammar. There is a craft to creating phrases, sentences, and paragraphs that ensure communication. An editor, with the vantage point of a reader, can contribute to this craft by looking for opportunities to improve sentence structure.

A sentence can make three types of statements:

• A subject does something (active verb)

Researchers write reports.

• A subject has something done to it (passive verb)

The reports are reviewed by editors.

• A subject is equal to something else (linking verb)

Reports are Langley's research product.

In all three types of sentences, the subject and verb are the most important elements. Since the subject and verb are the most important elements in a sentence, improving their relationship, clarifying the subject, or making the verb more vigorous will improve the sentence.

The importance of subject and verb may be an elementary idea, but the writer of the following sentences has surely forgotten it:

An indication of probable asymmetric throat area reduction between the upper and lower throats of this nozzle during reverse thrust operation is shown by the jet-lift coefficients presented in figure 28.

At NPR < 4, there is a large reduction in discharge coefficient due to reverse thrust operation, indicating a decrease in the effective throat area for the nozzle.

The subject of a sentence should be expressed with clear, concrete words; and in technical documents, it usually is. However, this clearly expressed topic of the sentence is often not the grammatical subject. In the first sample sentence, indication is not the true subject; in the second sample,

27 Back to Top

the subject and verb positions have been wasted by an indirect construction, there is.

Effective Revenue Writing 2 (Linton 1962) suggests that the real subject of a sentence can be found by identifying the real action in the sentence; the subject is then either receiving the action or preferably performing it. In the first sample sentence, identify the action. From among the several words of action (indication, reduction, operation, is shown, presented), indication seems most important. Two revisions come to mind when indicate becomes the main verb:

Asymmetric throat area reduction between the upper and lower throats of this nozzle during reverse thrust operation is probably indicated by the jet lift coefficients presented in figure 28.

The jet lift coefficients presented in figure 28 indicate a probable asyrnmetric throat area reduction between the upper and lower throats of this nozzle during reverse thrust operation.

Which sounds best? The second revision, with an active verb close to its subject, is certainly easier to read. Out of context, it is preferable. Context affects the choice of subject. For good transition from one sentence to another, the subject of a sentence should relate to the previous sentence.

Now consider the second sample sentence, containing the indirect construction. The expletive there forces the true action of the sentence, indicating, into a participial construction. Making indicate the main verb results in

At NPR < 4, a large reduction in discharge coefficient due to reverse thrust operation indicates a decrease in the effective throat area for the nozzles.

Another indirect construction involves the pronoun it:

As with any valid grammatical construction, indirect constructions sometimes serve a function, but many grammar and writing books criticize them as being wordy (see section 2.4.1) and unnecessary. Rowland (1962) states that "expletives serve only to mark time until the true grammatical subject appears." In Tichy and Fourdrinier's (1988) opinion, as well as in

28 Back to Top

Rowland's, indirect constructions can be ambiguous. Such idioms as "it is known" or "it is believed" indicate general knowledge or belief:

It is believed that this is a nozzle-aspect-ratio effect.

In most technical writing, these constructions refer to the author's belief or knowledge. Perhaps a personal pronoun is appropriate (see section 1.3.2):

We believe that this back pressure increase is a nozzle-aspect-ratio effect.

Note the change in the subordinate clause of this sentence. Demonstrative pronouns (this, these, that, or those used as nouns) with "broad reference" (Ebbitt and Ebbitt 1982) can be undesirable and ungrammatical when their antecedent is not clear (see section 1.3.1):

Please do not insert stock abstract words such as result, effect, or apparatus after every demonstrative pronoun. Remember that the subject of a sentence (or clause) should be clear and concrete and should relate to previous ideas.

2.2.2. Make Verbs Vigorous

The only words capable of expressing action are verbs and their derivatives. Invigorating verbs will make writing more concise and easier to read. In the following phrases, the action of the verb reduce is progressively deemphasized:

Active voice	If we reduce drag, . . .
Passive voice	If drag is reduced, ...
Verbal	With reduced drag, ...
Verb-derived noun	With reduction of drag, . . .

Weak verbs

One of the most common causes of weak verbs has already been discussed; when the real verb of a sentence becomes the subject, a weaker verb must be substituted:

29 Back to Top

Another method of weakening verbs is to hedge with such words as might, may, seem to, appear to, or tend to. Hedges not only weaken the verb, as they are meant to, but also imply indecision on the part of the author. They should not be overused (see section 2.4.1). 

Active versus passive voice

As discussed in section 1.4.3, writing authorities overwhelmingly prefer active voice to passive voice. However, Tichy and Fourdrinier (1988) list five situations when 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

• When a weak imperative is needed

Although the first two items justify much of the passive voice in technical documents, the converse of the fourth item must also be considered. In our passive voice reports, an occasional active voice sentence is needed for variety. (Tichy and Fourdrinier 1988 also discuss the importance of sentence variety to good style.) Thus editors should watch for sentences that could appropriately be revised to active voice:

30 Back to Top

The active version of the last example ascribes a human ability (to show) to an inanimate object (figure), a rhetorical device commonly called personification. Rowland (1962) states, "Personification, if not overdone, is an effective means of conferring vigor and emphasis. . . and affords relief from excessive use of passive voice." Bernstein (1981) agrees, but both caution against ludicrous attributions (called pathetic fallacy); for example,

Linking verbs also can sometimes be converted to active voice:

Verbals

Active writing does not require active voice, since there are other types of active constructions (Linton 1962):

Prepositional phrase:	methods for reduction of...
Gerund phrase:	methods for reducing...
Infinitive phrase:	methods to reduce...

The emphasis on the action increases from the prepositional to the gerund phrase and from the gerund to the infinitive phrase.

2.2.3. Improve Subject-Verb Relationship

The subject and verb should be the most important elements of a sentence. Too many modifiers, particularly between the subject and verb, can over-power these elements. If modifiers are more interesting and active than the sentence itself (subject-verb-object), the action of at least some modifiers should be transferred either to the main verb or to a new sentence or independent clause:

31 Back to Top

When placed between the subject and verb, too many modifiers can ruin the continuity of the sentence. A reader may not be able to recall the subject by the time the verb comes along. Adverbial modifiers can often be moved, but adjective phrases and clauses present a special problem because they cannot wander far from the noun that they modify:

Pressures that were sensed at discrete locations such as in the cavity just behind the seal, at the bulkhead, and at the base of the elevon and ramp are also given.

When a long adjective phrase or clause intrudes between the subject and verb, four choices for revision are available:

• Shorten the intervening adjective:

Pressures sensed at discrete locations, such as at the bulkhead, are also given.

• Invert the subject and verb:

Also given are pressures that were sensed at discrete locations such as in the cavity just behind the seal, at the bulkhead, and at the base of the elevon and ramp.

Inverting a sentence drastically changes emphasis and often sounds artificial.

• Place the verb between the subject and the adjective if the verb phrase is short and modification is clear:

Pressures are also given which were sensed at discrete locations such as in the cavity just behind the seal, at the bulkhead, and at the base of the elevon and the ramp.

We realize that it is ungrammatical to place a verb between a relative clause and its antecedent. Effective Revenue Writing 2 (Linton 1962) condones this infraction as long as modification is clear.

32 Back to Top

• Change the adjective clause to an adverbial phrase

Pressures are also given for discrete locations such as in the cavity just behind the seal, at the bulkhead, and at the base of the elevon and the ramp.

Changing adjectives to adverbs often changes meaning.

2.3. Parallelism

Parallelism is an important and often neglected syntactic consideration. To quote Tichy and Fourdrinier (1988),

A major device for sentence emphasis is parallel construction. Equal thoughts demand expression in the same grammatical form. Repetition of structure within a sentence is a most effective device for making the long sentence easy to read, and repetition of structure in two or more sentences connects them. An understanding of parallelism is therefore essential for emphasis and coherence.

When should sentence elements be parallel and how do we make them so? When two or more ideas are logically equal, they should be made parallel by writing them in the same grammatical structure. Grammatically, words are equal (parallel) to words, phrases to phrases, subordinate clauses to subordinate clauses, and independent clauses to independent clauses. Parallel grammatical elements are also called "coordinate."

Logic dictates the use of parallelism, or coordination. For example, the two coordinate clauses in the following sentence are not logically equal:

The compressor may be operated in the compression mode and then the flow is expelled from the anechoic room to the test duct.

This sentence calls for subordination, not coordination:

When the compressor operates in the compression mode, the flow is expelled from the anechoic room to the test duct.

Except for coordinate clauses, such as the example above, sentence elements that are not logically parallel are rarely found in parallel construction. However, logically parallel ideas are often not written in grammatically parallel structure.

2.3.1. Connectives Requiring Parallelism

Effective Revenue Writing 2 (Linton 1962) lists four types of connectives requiring parallelism coordinate conjunctions (and, or, but), correlative conjunctions (either . . . or, both . . . and, not only . . . but also), conjunctive adverbs (therefore, otherwise, however), and the semicolon used to connect independent clauses.

Coordinate conjunctions probably provide the most opportunities to use parallelism. As discussed in section 1.8.1, they join words, phrases, and clauses of equal grammatical rank. Coordinate clauses joined by a

33 Back to Top

coordinate conjunction should be logically equal. Similarity in grammatical structure, if possible, is also a good idea. For example, the voice of the verb might be kept the same:

Correlative conjunctions demand strict parallelism: Both elements of the correlative must be followed by the same part of speech (see section 1.8.1).

Independent clauses joined by conjunctive adverbs or simply by a semicolon should also be logically coordinate; however, grammatical parallelism is an option to be used for emphasis or contrast:

In the compression mode, the duct serves as an eductor; in the exhaust mode, it serves as an inductor.

2.3.2. Itemization

As mentioned earlier, repetition of structure is effective in making long sentences easy to read. Itemization is another important device for making a sentence containing several long parallel elements easy, perhaps possible, to read. Itemization can also be used to emphasize the individual parallel elements.

Itemization is a special form of parallelism. The introductory phrase or clause leading into the list should read logically into each item:

The test indicated

1. That continuous thermal exposure degraded the strength of the composite material.
2. That cyclic thermal exposure did not degrade the strength of the composite material.

In the above example, the common element, that would usually be included in the introductory clause: "The test indicated that."

In an itemization, all items must be the same grammatical construction, for example, all prepositional phrases, all noun phrases, or all complete sentences:

34 Back to Top

2.4. Brevity and Conciseness

Technical writing should be concise, free of redundancy and unnecessary detail. Minimizing the number of words to achieve brevity does not necessarily result in conciseness and may destroy the emphasis, the pace, and perhaps the meaning of a passage. However, wordiness seems to be a common fault of technical writing, and editors should delete unnecessary or redundant words.

2.4.1. Wordiness

Many reference books contain sections containing lists of wordy, redundant, or trite expressions (for example, Skillin et al. 1974, p. 407ff; and Rowland 1962, chapter XIV). We suggest that writers and editors occasionally peruse such lists in order to remain sensitive to unnecessary wordiness. Tichy and Fourdrinier (1988) classify seven types of common wordiness and list numerous examples of each:

• Tautology, the unnecessary repetition of an idea

• Dilute verbs (see section 2.2.2)

• Hiccups, superfluous prepositions and adverbs

• Roundabout constructions

35 Back to Top

• Hedging and intensifying

• Unnecessary intensifiers

more dominant
quite impossible
very unique

• Pointless words and phrases

It is interesting to note that
It might be stated that
In the case when

• False elegance

36 Back to Top

Occasionally, a passage may be wordy, to the point of being difficult to read, or it may exceed a limiting number of words (for example, NASA limits abstracts to 200 words). Linton (1962) suggests five ways to economize:

• Reduce syntactic weight by subordinating sentences, changing subordinate clauses to phrases, and reducing phrases to adverbs and adjectives:

Any ash that was not carried into the stratosphere moved toward the northeast into a bank of mammatus clouds. Mammatus clouds have downward accelerations and upward velocities. They thus allow the larger particles to drift downward.

Any ash not carried into the stratosphere moved northeasterly into a bank of mammatus clouds. The downward acceleration and upward velocity of these clouds allowed the larger particles to drift downward.

• Avoid redundant and roundabout phrases (see section 2.4.1).

• Avoid passive voice (see section 2.2.2).

• Prefer active verbs to verbs expressing state of being, that is, linking verbs and such words as appear and seem.

• Combine ideas of several sentences into one. Of course, avoid long, confusing sentences; but many short, simple sentences waste words:

There were three distinct flow characteristics. Ahead of the wing, a bow wave of water droplets was observed. On the wing surface, a continuous water film formed. Between 16.7 and 41.7 percent of the chord, the film broke down into discrete runoff streams.

The three observed flow characteristics were a bow wave of water droplets ahead of the wing, a continuous water film on the wing surface, and discrete runoff streams beginning at 16.7 to 41.7 percent of the chord.

Conciseness is especially important in titles; a short title improves the appearance of the cover and a precise title indicates what readers can expect to find inside the cover. Brevity and preciseness must be balanced so that in a minimum number of words, the title is correct (it presents the topic of the paper), complete (it expresses the limits of the paper), comprehensible (potential readers will understand it), and concise (it is as efficient as possible).

A title which passes this evaluation (from Rathbone 1985) may be anything but brief. Rathbone also suggests that titles be shortened by deleting familiar phrases which concern reporting or information gathering. Such phrases as

An Investigation of ...
An Analysis of ...
Conference on ...

37 Back to Top

can often simply be dropped without changing the meaning of the title. Unnecessary articles should also be deleted. Often a title becomes lengthy and awkward because several prepositional phrases have been added to qualify it. Several approaches can be taken. A prepositional phrase can be changed to a unit modifier:

Note: In this title, analysis cannot be deleted because using modifies it.

• Care must be taken to keep the title comprehensible. A string of unit modifiers can be as awkward as a series of prepositional phrases, and far more ambiguous.

Another approach for reducing the number of prepositions is to make subtitles:

Note: This revision not only removes a prepositional phrase, but also emphasizes the theme of the paper.

A title can be livened up and prepositions removed by changing verb-derived nouns to verbals, for example,

Of course, titles must not be shortened indiscriminately. Keep in mind the goal of maximum information in a minimum of words. In the previous example, use was not changed to deflect with brevity in mind. However, the word deflect adds to the spirit of conciseness because it means more. Consider replacing or clarifying words with vague meaning such as method,

38 Back to Top

system, facility, use, or approach. The following example illustrates this point:

The revision is two words longer, but it seems more concise because it says so much more with only two more words.

2.5. Comparisons

Comparisons are of major importance in technical writing; experimental results are compared with predictions, results at standard or control conditions with results at test conditions, full-scale data with model-scale data, characteristics of one configuration with those of another. Such comparisons can be complicated and therefore should be expressed as simple, straight-forward constructions.

The most frequent problem with comparison is ambiguity concerning the items being compared:

2.5.1. Comparison of Adjectives and Adverbs

Adjectives and adverbs change form to indicate degree of comparison (IRS 1962):

• Positive degree merely indicates existence of a quality.

• Comparative degree indicates a quality existing to a greater or lesser degree in one thing than in another.

• Superlative degree indicates a quality existing to the greatest or least degree in a group of things.

Comparative degree is formed by adding the suffix er or adding more or less before the modifier. Superlative degree is formed by adding the suffix est or adding most or least before the modifier.

Most adjectives with three or more syllables and almost all adverbs are compared by adding more and most (or less and least). In addition,

39 Back to Top

some modifiers, for example, good, have irregular comparisons; the words themselves change:

Positive	Comparitive	Superlative
high	higher	highest
dependable	more dependable	most dependable
carefully	less carefully	least carefully
good	better	best
far	farther, further	farthest, furthest

• The comparative degree is used to compare two persons or things or to compare a person or thing with a class:

Pressures were higher on the left nozzle than on the right nozzle.

The values from the second test varied more than those from the first test.

Pressures were higher at orifice 7 than at the other 47 orifices.

Note the use of other in the last example; either other or else is required when a person or thing is compared with a class in comparative degree.

• The superlative degree is used to compare more than two persons or things. The word all (not any) is used with superlative degree for comparison with a class.

Of four nozzle configurations, the dry power nozzle experienced the highest pressures.

The values from the eighth test varied most.

Pressures at orifice 7 were highest of those at all 48 orifices.

Tichy and Fourdrinier (1988) discuss several types of errors which obscure meaning in comparisons: incomplete comparisons and omission of standard are often encountered in technical writing.

Incomplete comparisons

Unless all necessary words are included, many comparison sentences have two meanings:

40 Back to Top

Demonstrative pronouns are often used to complete comparisons (see section 1.3.4):

If the antecedent of the demonstrative pronoun is obscure, reword the sentence or repeat the subject of comparison.

Omission of standard of comparison

Unless the standard of comparison is clear, comparisons are meaningless:

2.5.3. Comparison Constructions

So far in this section, only comparison constructions involving than have been discussed. Several other constructions may be used, or misused, to express comparisons.

Compare with

The verb compare takes either to or with, depending on meaning. Bernstein (1981), explains the use of with quite clearly "When the purpose is to place one thing side by side with another, to examine their differences or their similarities, use with." In technical writing, do comparisons ever have any other purpose?

The participle compared with is often used (sometimes in a dangling construction) when another construction would be better:

41 Back to Top

As... as

The correlative construction as ... as is an excellent method of indicating similarity, or dissimilarity:

The ferritic steels are not as tough at cryogenic temperature as at room temperature.

The second as should not be omitted when a comparative degree rmodifier intervenes:

Different

The adjective different is often used superfluously:

Note that different should not be indiscriminately deleted. The above sentence could have meant

Figure 16 presents data from two wind-tunnel runs at different conditions.

When possible, change the predicate adjective different to the verb differ, a more vigorous construction (see section 2.2.2):

The trends on the lower surface are different from those on the upper surface.

The trends on the lower surface differ from those on the upper surface.

42 Back to Top

• Different takes the preposition from:

Bernstein (1981) explains the rare occasions when different than is appropriate to avoid the elaborate construction from that which:

In error analysis, standard deviation may be calculated with a different equation than in statistical analysis.

Just as demonstrative pronouns are sometimes needed to cornplete a comparison (section 2.5.2), they are sometimes needed with different:

The..., the

An effective method of comparison is the idiomatic correlative construction involving the ..., the:

The lower the temperature, the more brittle the steel becomes.

The subject of sentence emphasis is often neglected by authors and editors. Many writers must resort to underlining (or italicizing) to emphasize an idea because they do not understand methods of emphasis (see section 3.9.1). Editors who do not pay attention to emphasis cannot assist these authors and, worse yet, may overlook the effect that editorial revisions have on sentence emphasis.

"Any sentence markedly different from the preceding sentences receives stress-a short sentence after several long ones; a periodic sentence after loose sentences; a simple sentence after a series of complex, compound, or compound-complex sentences" (Tichy and Fourdrinier 1988). Be sure that a contrasting sentence contains an important idea.

2.6.1. Emphasizing With Sentence Structure

The above quote from Tichy and Fourdrinier illustrates a most effective method of emphasis parallelism. As discussed in sections 1.8.1 and 2.3, parallelism is grammatically required at times. It can also be used to emphasize the likeness or contrast between items. In parallel constructions, emphasis on the individual parallel items can be increased by repeating articles, prepositions, or introductory words:

43 Back to Top

Pressure distributions were obtained on the wing, elevon, and cove walls.

Pressure distributions were obtained on the wing, on the elevon, and on the cove walls.

The study indicated that thermal cycling caused matrix cracking and fatigue cycling caused no damage.

The study indicated that thermal cycling caused matrix cracking and that fatigue cycling caused no damage.

Of course, the most emphatic way to list parallel elements is to itemize them:

The study indicated that

1. Thermal cycling caused matrix cracking.
2. Fatigue cycling caused no damage.

Positions of emphasis in a sentence are the beginning and the end. Therefore, if a modifying phrase is moved to the beginning of a sentence, that phrase receives emphasis:

Cove cold-wall heating rates at zero leakage decreased from 2 percent of the wing heating rate.

At zero leakage, cove cold-wall heating rates decreased from 2 percent of the wing heating rate.

Emphasis can be added to internal sentence elements by moving them to an unusual position:

After each session of noise, the subjects rated overall noisiness, among other things.

After each session of noise, the subjects rated, among other things, the overall noisiness.

Be careful not to misplace the modifier:

After each session of noise, the subjects, among other things, rated the overall noisiness.

Rhetorical connectives, such as however, therefore, hence, and thus, can serve to emphasize elements of a sentence. Placing such adverbs within a sentence emphasizes the words immediately preceding them (Linton 1962):

However, isothermal exposure did increase ductility in the matrix material.

Isothermal exposure, however, did increase ductility in the matrix material.

44  Back to Top

Isothermal exposure did, however, increase ductility in the matrix material.

Commas around such adverbs may be omitted to decrease emphasis, and of course commas would never be used around these adverbs when they are restrictive (Rowland 1962):

Isothermal exposure thus increased ductility in the matrix material.

As indicated above, commas around rhetorical adverbs and other interrupting elements (section 3.5.2) increase emphasis on the enclosed element. A comma between coordinate adjectives adds emphasis to the adjectives as separate modifiers:

The delta function has a long, controversial history

Replacing tire comma with and further increases this emphasis:

The delta function has a long and controversial history

Note however that only coordinate adjectives can be punctuated this way (see section 3.5.1).

Other marks of punctuation affect emphasis. Using a colon to introduce a list tends to emphasize the list:

The scatterometer is separated into a gimbal, a transmitter-receiver assembly, and rack-mounted electronics.

The scatterometer is separated into three assemblies: a gimbal, a transmitter-receiver assembly, and rack-mounted electronics.

The dash, when used carefully, is an emphatic mark-it can be used to emphasize interrupting elements, nonrestrictive modifiers, and explanatory phrases and clauses (see section 3.6):

Auxiliary meteorological data used herein - such as vorticity - have been computed from NMC isobaric height fields.

The one-sided spectrum - engineers call it simply "spectrum" - is the output of most spectral analyzers.

Other random processes have average properties that vary appreciably with time - for example, the load demand on an electric power generating system.

45

+ Contents   |   + Back to Top   |   + Previous Section   |   + Next Section