Parallel structure and comparisons
Words, phrases and clauses of equal rank in a sentence take the same grammatical form, and a comparison sets side by side the terms the writer meant to compare; where either fails, the reader has to realign the sentence. Where coordinated parts are not of equal importance, the mismatch is repaired not by matching them but by demoting the lesser one so that the other is emphasised.
Elements of equal rank
Sentence elements of equal rank — words, phrases and clauses that are coordinate, items and ideas of equal importance, elements that have the same function or express similar ideas — should be expressed in the same grammatical form. As a general rule, nouns should be parallel with nouns, participles with participles, gerunds with gerunds, infinitives with infinitives, clauses with clauses, and so on. He likes bicycling, canoeing, and to go on hikes uses two gerunds and an infinitive phrase where three gerunds would do: he likes bicycling, canoeing, and hiking.
Proper parallel structure makes it easier for the writer to say exactly what is meant and for the reader to work out what was meant, and makes the text more pleasant to read, so the AMA Manual of Style instructs medical communicators to attend to it. It also makes complex sentences easier to understand. Ideas are easier for the reader to follow if they are presented in a similar pattern, so the same ideas should be written with the same grammatical structure. Parallel construction guides the reader, providing clues to equivalent ideas by putting them in equivalent grammatical constructions, and helps the reader organise concepts and see relationships quickly. It also aids the rhythm and flow of the writing and helps make it clearer. It matters in sentences, particularly long ones, as well as in lists.
One textbook of scientific writing counts the lack of parallelism among the most disturbing deficiencies in scientific texts, and observes that both native and non-native speakers of English find nonparallel structures difficult to avoid. Careful phrasing and the use of short sentences can help avoid such errors from the beginning.
Reviewing the parts of speech and the basic rules of English syntax makes faulty parallelism and faulty comparison easier to recognise and correct, and besides the underlying principles an editor must learn the grammar terminology, which enables them to explain to an author why a given change is needed.
Five constructions call for thinking about parallel structure: elements joined by a coordinating conjunction; items being listed, whether inside a sentence or in a bulleted list or a table; items linked by correlative conjunctions; comparisons; and verbs of being.
Coordinating conjunctions and lists
The main coordinating conjunctions in English are and, but, or, nor and for, and they are so called because what they join is of equal grammatical rank — which is why the joined elements ought to take the same form. Surgery, radiation therapy, and to give chemotherapy are possible therapeutic approaches is corrected to surgery, radiation therapy, and chemotherapy.
In a bulleted list or among the elements of a table the conjunction is implied, and the same requirement still applies: all phrases or all sentences, all statements or all commands, all verbal phrases or all nouns. The items of a series inside a sentence should take identical grammatical structures. The items should also stand in a logical order — alphabetical, by importance, by time sequence or some other order. If the items in a bulleted list or a table cannot be made parallel, ask whether they really constitute a list at all; it might make sense to separate them into two or more lists or to rewrite the section as a paragraph.
A list of writing tips each written as a complete thought in the imperative — know your audience, read and follow the instructions to authors, use, but do not trust, spell-check programs — lets the reader attend to the content of each tip rather than trying to sort the tips into categories or groups, because the parallelism has already done the sorting. Medical writing ranges from editing patient education materials, physician EMR help manual writing, to creating clinical research protocols, to writing of pharmaceutical information sheets and other treatment and therapy pertaining instructions presents several items, presumably all of equal importance, in a variety of grammatical constructs, and the reader has to strain to work out what is being said; the rewrite makes them one series — medical writing involves editing and writing many kinds of documents including online help files for EMR software, clinical research protocols, pharmaceutical information sheets, and patient-directed materials. He is an expert in studying the sleeping pattern in adolescents, observing the REM sleep behavior in adults, and to develop strategies for improved sleeping quality puts an infinitive after two gerunds, and is corrected either with three gerunds — and developing strategies — or with three nouns — the study of…, the observation of…, and the development of….
Correlative conjunctions
Correlative conjunctions are pairs that work together — either… or, neither… nor, both… and, not only… but also and whether… or — and errors in parallelism often occur with them; the structure following the second half should mirror the structure following the first. Either always goes with or and neither always goes with nor, and the pairs can link more than two elements, as in neither snow nor rain nor heat nor gloom of night stays these couriers…. The placement of prepositions in these constructions needs particular attention: poor drug efficacy may be caused by either lack of absorption or by increased clearance repeats the preposition on one side only, and dropping the second by fixes it. The reviewers criticized not only the layout of the tables but also they criticized the length of the article becomes not only the layout of the tables but also the length of the article; either we can use the validated assay or not becomes either we can use the validated assay, or we cannot; and they neither applied proper statistics, nor did they report standard deviations becomes they neither applied proper statistics nor reported standard deviations. It was both a complex experiment and very time-consuming joins a noun to an adjective, and the experiment was both complex and time-consuming makes and connect two adjectives. The protocol is both a long procedure and very tedious is rewritten as the protocol is long and tedious.
Verbs and adverbs
Parallel structure covers verbs, adverbs and other parts of speech as well as subjects. During study visits, the subjects received the study drug, completed a quality of life questionnaire, and had a physical examination keeps every verb in the same tense and maintains past-tense verb, then article, then noun throughout. Where a sentence uses more than one verb, the verbs should be kept parallel by not shifting tense or between active and passive voice: Prof. Higgins wrote his lecture on the train, and it was presented by him at the medical school only one hour after his arrival becomes Prof. Higgins wrote his lecture on the train and presented it at the medical school only one hour after his arrival. A single verb form shared by two helping verbs breaks the parallel: the department has in the past and will in the future expand the new learning tool becomes has expanded the new learning tool in the past and will continue to expand it in the future.
After each dose adjustment, patients were asked to record their pain levels hourly during the first day, daily during the first week, and weekly thereafter maintains an -ly adverb followed by a prepositional phrase. Patients recorded their pain levels every hour, for the first day, then daily for the first week and finally once a week thereafter is made easier to read by using parallel structure and describing the dosage routine with adverbs: patients were asked to record their pain levels hourly for the first day, daily for the first week, and weekly thereafter.
Equivalent and non-equivalent coordinated units
Coordination nonparallelism is the lack of structural symmetry between coordinated sentence constituents that are intended to be equivalent in importance, of which a classic example is I love fishing, swimming, and to run. Nonparallelism is of two general types, and each takes its own revision. Nonparallelism between equivalent units is a dissonance, which can be revised by transforming the nonparallel unit into a parallel one. Nonparallelism between non-equivalent units impedes immediate comprehension, and can be revised by de-coordination: transforming the less important unit into a lesser syntactic structure so that the other coordinated unit is emphasised. The nonparallelism is thus a cue that the units are not intended to be viewed as of equivalent importance.
The abundant detail in research writing is amenable to coordination, during which nonparallelism occurs both between core sentence constituents such as nouns and verbs and between non-core constituents such as modifiers; for most instances of nonparallelism the rhetorical consequence is dissonance. In I love fishing, swimming, and to run comprehension is not impeded, because all three are sporting activities.
This technique depends on biological molecules binding to other molecules reversibly and with high specificity coordinates the adverb reversibly with the adverbial prepositional phrase with high specificity, and turning the phrase into the adverb specifically makes the two parallel. Nonparallelism between an adverb and an adverbial is a minor distraction of dissonance, but when students compare a nonparallel example with a parallel revision in a principle-testing option exercise, most select the revision. Coordinating the noun epidemics with the nominal the eating of dinosaur eggs by early mammals may be a more serious distraction, possibly because nouns are core sentence constituents functioning as subjects, direct objects and subject complements. It can be repaired by replacing the second constituent with the parallel noun mammalian-oophagy, or by de-coordination, making epidemics the object of the phrasal preposition in addition to, which eliminates the need for parallel structure and may better express how the pieces of information relate. De-coordination, however, de-emphasises epidemics as if it were the more understood of the two causes, so that the eating of dinosaur eggs by early mammals becomes the focus of the hypothesis.
The most common nonparallelism in research writing occurs between coordinated verbs that differ in type — linking, transitive or intransitive — and its revision often involves transformation into another syntactic pattern. Lysine is an abundant muscle constituent, and decreases in amount during starvation coordinates a linking verb with an intransitive one, and the apparent equivalence of structure overemphasises the descriptive clause and deemphasises the assertive one. Reducing the independent clause to an appositive gives lysine, an abundant muscle constituent, decreases in amount during starvation, which deemphasises the description and emphasises the assertion. Such a coordination is often mistakenly marked with a comma, which is itself distracting because the comma disrupts the coordination. In spot no. 1 was the most acidic and had the highest apparent molecular weight neither verb is emphasised, because coordination renders them equivalent, yet the nonparallel verb type is a cue that the relation is non-equivalent: the linking verb usually marks the less important descriptive information compared with the assertive information marked by the transitive verb. The first revision demotes the linking-verb information to a reduced adjectival phrase in apposition — spot no. 1, the most acidic, had the highest apparent molecular weight — while an alternative revision lists the properties, because they are seemingly independent of each other and of equivalent importance: the properties of spot no. 1 were as follows: most acidic; highest apparent molecular weight.
Coordinating a passive with an active verb is a cue that a de-coordinated structure would better match the rhetorical intent. Traditional dose studies are performed at a pollutant concentration much higher than that observed in situ and depend on mortality as a final criterion can be revised by attenuating are performed into the past participle performed, or by demoting depend on mortality as a final criterion into the present participial phrase depending on mortality as a final criterion. In each revision the phrase with the finite verb receives the emphasis and the modifying phrase is deemphasised, so the choice may depend on which information is intended to be emphasised. The length of the modifying phrase is another determinant: both revisions interpose a phrase between the subject and the verb, the first by twelve words and the second by seven, so on that basis the second may be the selection. A third revision places the participial phrase before the subject and avoids disrupting the subject–verb sequence altogether.
Identifying and revising nonparallelism is often done at the superficial level, simply revising the nonparallel structure of the coordinated unit; deeper insight into the meaning of the information may elicit another pattern, not coordination, that matches structure and rhetorical intent more effectively. An evolution from coordination to another syntactic pattern is not unexpected, because coordination is one of the first stages of syntactic fluency to develop.
Comparisons and antithesis
Comparisons often involve the conjunction than, the construction as… as or a verb of being, and they can be marred by faulty parallel structure, by faulty comparison or by both. Faulty parallel structure means the items compared are not in the same grammatical form; faulty comparison means the items compared are not the ones the writer meant to compare. The results of this study are similar to the Nurses' Health Study compares results with a study; similar to the results of the Nurses' Health Study fixes the comparison, and similar to those of improves it further with a demonstrative pronoun. Faulty comparisons often come from an elliptical construction in which words have been left out — he is closer to his father than his mother resolves either as than to his mother or as than his mother is. An editor who finds such an ambiguous sentence should query the author, not guess.
The word than needs particular attention: an editor can search the document for every instance of it, look at what is being compared on each side, and consider moving the compared items as close to the word as possible, so that treatment with A was associated with more pronounced antidepressant effects during the first weeks of treatment than B becomes during the first weeks of treatment, antidepressant effects were more pronounced in the group treated with A than in the group treated with B. Other comparisons can be found by searching for the string compar, which catches compare, compared and comparison at once. A compared with phrase is adjectival and will try to modify whatever noun it directly follows, and sometimes than in is better: heartworm infection is more common in dogs compared with cats becomes more common in dogs than in cats.
The time to treatment failure was 12.2 months in the group treated with drug X, compared to 3.1 months in the placebo group is a construction common in writing by non-native English speakers, and it makes the reader stop to realign the information. The repair realigns it so that the reader does not have to, either by making both halves xx months in the xx group — 12.2 months in the drug X group and 3.1 months in the placebo group — or by reducing it to with x: the time to treatment failure was longer with drug X than with the placebo (12.2 vs. 3.1 months).
A verb of being works like an equal sign, so the test is to ask what the sentence is equating and whether the elements on either side can be put in the same grammatical form.
In an antithetical construction, something is true of one thing but not another, set up with but not or rather than, and as with comparisons both parts should be parallel: the study administration approved the students' right to skip some of their lectures but not postponing the final exam becomes but not to postpone the final exam.
Ellipsis in comparisons
Dissonant nonparallelism occurs in two patterns of comparison: the typical adjective-based pattern — x is similar to y, there is more x than y — and the less common correlative conjunction-based one, the more x… the more y, which functions as a correlative conjunction similar to not only… but also.
A noun elided out of an adjective-based comparison. The masticatory apparatus of a bird is similar to a human appears to compare the apparatus with a human rather than with the masticatory apparatus of a human; such comparisons often lack the second noun or noun phrase, though it is implied, and the frequency of the pattern may make the implicit meaning understandable. In one repair, the demonstrative pronoun restores the parallel — similar to that of a human — and elicits backtracking, though the sentence pattern is familiar. In the other, the sentence is rebuilt so that the compared nouns are structurally equivalent and at the sentence-end position of emphasis: there is a similarity between the masticatory apparatus of a bird and a human.
The related construction the masticatory apparatus of a bird and a human are similar ends on similar, which prompts the question similar to what?; the plural verb after the singular apparatus is grammatical because of the plural modifiers, a plurality that may be notional, singular in form but plural in context. A bird's masticatory apparatus is similar to a human's is parallel in its possessives but infrequent, which may result from the informality of the possessives and the distance between them; as with ending on similar, a sentence ending on human's seems incomplete.
A verb elided out of an adjective-based comparison. Renal erythrocytes transferred more DHA to the foetus than foetal plasma reads as though more DHA was transferred than foetal plasma was, because verb ellipsis, a comparison missing its second verb, causes confusion about what is being compared. The verb do is often used to avoid repeating the verb in a comparison, but, as with other concision techniques such as vice versa, it makes the reader backtrack to determine what it means; supplying did makes the verbs parallel but elicits that backtracking and an unfamiliar subject-to-verb inversion. Recasting into the passive — more DHA was transferred to the foetus by renal erythrocytes than by foetal plasma — emphasises the comparison through the sentence-end position of the compared nouns and the repetition of the preposition by. The expletive variant, there was more DHA transferred to the foetus by renal erythrocytes than by foetal plasma, conveys a typical results-section pattern, first identifying an observation and then stating the comparison; both versions focus thematically on more DHA transferred rather than on the narrative that something does this and another thing does that.
Too little ellipsis in a correlative comparison. In the more that paths are used for routing, the more secure that the network is, the passive verb phrase in the clause conveying the condition is nonparallel to the linking verb in the clause conveying the consequence. The repair removes rather than adds: the more paths for routing, the more secure the network. This verb-free compound sentence is neither uncommon nor ungrammatical: the frequency of the pattern, mostly in its elliptical form, is evidence of its grammaticality. Its combination of succinctness and parallelism is memorable.
A correlative conjunction that changes direction. The more that collagen is in a triple helical arrangement, the more that it resists denaturation, and the less that it is solubilised by acetic acid turns at the third clause. Where the first two correlative clauses run in one direction and the third runs in the other, the nonparallelism is distracting; with only two clauses, a reciprocal relation such as the more… the less is only slightly distracting. The full repair makes the third clause match — the more that it resists solubilisation by acetic acid — and the elliptical one deletes the complementising that and the redundant the more it resists: the more collagen in a triple helical arrangement, the more its resistance to denaturation and solubilisation by acetic acid. The parallelism between the correlative conjunctions is what lets denaturation and solubilisation be coordinated.
The cause of the nonparallelism may differ between the two comparison patterns. Ellipsis of a compared noun or verb seems to cause the adjective-based failure, so the repair adds the elided element back — with the demonstrative that or the filler verb do — or transforms the syntax into an end-of-sentence comparison, which enables a thematic subject. Lack of ellipsis may cause the correlative failure, since its revision involves a shift to an elliptical verb-free option; and where the conjunction itself is nonparallel, replacing it is as straightforward a revision as it is for nonparallel coordination. Adjective-based comparison distractions may not be section-specific, having turned up in an introduction and in a results section, while both correlative examples came from introductions.