Parallelism in Writing

What is parallel sentence structure?

A parallel sentence structure refers to words, phrases, or clauses in the same sentence having the same grammatical form. Parallelism encourages natural flow and is most often applied to sentences that are either listing elements or comparing elements. Parallel sentence structure should also be applied to headings and section titles in academic papers.

Both of the above sentences list elements. The elements listed by the first sentence are “books,” “writing,” and “painting.” While “writing” and “painting” have the same grammatical form (gerunds), “books” does not (common nouns). As such, this sentence comes off as awkward and somewhat unbalanced. The elements listed by the second sentence are “reading,” “writing,” and “painting.” These elements all share the same grammatical form, and therefore the sentence reads naturally and gives the reader a sense of rhythm.

These two sentences are comparing elements. The elements compared by the first sentence are “visiting the office” and “email.” These two elements have different grammatical forms (verb phrase and noun). On the other hand, the elements compared by the second sentence – “visiting the office” and “sending us an email” – share the same form.

As mentioned above, elements in a list (or a series) should share the same grammatical form. These elements may be words, phrases, or clauses and are typically connected with the use of commas or semicolons in combination with conjunctions, such as “and” or “or.”

Parallel series of words

When the listed elements are words, the first step to enforcing parallel structure is ensuring that the elements are of the same word type. In other words, nouns should be listed with other nouns, adjectives with other adjectives, and verbs with other verbs.

If the listed items are verbs, they must all be of the same form. For example, a verb in the infinitive form must be listed with other verbs in the infinitive; it should not be listed with participles or gerunds.

Parallel series of phrases

When verbs are listed in series, they are typically in the form of verb phrases. As with elements that are single verbs, elements that are verb phrases must also be of the same grammatical form. In other words, infinitive phrases should be listed with other infinitive phrases, participle phrases should be listed with other participle phrases, gerund phrases should be listed with other gerund phrases, and so on.

“Greeting clients” and “updating the company calendar” are gerund phrases. However, “to answer the phone” is an infinitive phrase. By turning the infinitive phrase “to answer the phone” into the gerund phrase “answering phone calls,” parallel structure is maintained.

Parallel series of clauses

The same principle applies to elements that are verb clauses; all elements must be of the same grammatical form.

“That they should not run in the halls” and “that they should not chew with their mouths open” share the same grammatical form. However, “to use profanities” does not. To enforce parallel structure, it is necessary to alter “to use profanities” so that it has the same grammatical form as the earlier clauses. Or, alternatively, the other two clauses could be altered to have the same form as “to use profanities.”

Parallel lists after colons

Lists that come after colons must also have parallel elements.

As is the case for elements in a list, elements in pairs must also be parallel. Elements in pairs may be connected by coordinating conjunctions, correlative conjunctions, or comparative words. There are seven coordinating conjunctions: and, or, nor, but, yet, so, for. All of these can be used to connect elements into pairs. As is the case for lists, both elements in the pair must share the same grammatical form.

Correlative conjunctions are pairs of words that connect elements in a sentence. There are five correlative conjunctions: either…or, neither…nor, whether… or, not only… but also, both…and.

Two elements that are being compared in a sentence must also be parallel. Elements are compared using words such as “than,” “as,” “like,” and “over.”

The section headings of a given academic paper should have the same grammatical structure. Although journals do not typically state this as part of their author guidelines, enforcing parallel structure in section headings helps a paper come off as more professional and organized. The same applies to a paper’s outlines.

A sentence can have elements with the same grammatical form yet still be non-parallel if the elements are not consistent or compatible. All elements in a sentence should be clearly related to one another.

Grammatically, “found that the experimental results agreed with the theoretical model” and “went out dancing in the city” are of the same form. However, it is unclear how these two elements are related to one another. For proper parallelism, the connection between the two elements must be clear.