How to Create Clear Patterns with Parallel Structure

Clear sentences support clear scientific and medical writing. To craft clear sentences, you need to construct them in a way that is easy for readers to follow and understand. You can do this by using patterns in your writing.

A common pattern in writing is parallel structure (or parallel construction). With parallel structure, information follows the same grammatical pattern in a sentence. This structure makes the information easier to read and remember, enhancing the readability of your writing. 

Parallel structure can appear in many formats, including lists, verb forms, and the order of information. 

Lists in Sentences

When listing items in sentences, you want to ensure they use the same structure.

Consider the following example:

Example 1.1

Autism has a complex genetic basis with incomplete penetrance, a large number of susceptibility genes, and the complex gene-environment interactions.

 This example has three items in the list.

1.    incomplete penetrance
2.   a large number of susceptibility genes
3.   the complex gene-environment interactions

These items each have different articles. The first item has no article, the second item has the article a, and the third item has the article the. Because these articles are different, the structure is not parallel. This unparallel structure takes more effort to read and remember, creating more work for readers.

To make the list parallel, you can revise the items to have the same article.

Example 1.2

Autism has a complex genetic basis involving incomplete penetrance, many susceptibility genes, and complex gene-environment interactions.

In this revision, all the items in the list do not have an article, so the list runs parallel. The information in this version will be easier for readers to read and remember.

Lists in Bullets

Bullet points are another common format for lists.

Consider the following example:

Example 2.1

In the laboratory, students will learn how to:

• Cell culture

• Run Western blots

• Fluorescence microscopy

In this example, the second bullet starts with a verb, but the first and third bullets do not have verbs. To make the bullet points parallel, you want to revise them so that they all start with a verb (option 1) or none of them start with a verb (option 2).

For option 1, you can add a verb to each item in the list.

Example 2.2

In the laboratory, students will learn how to:

• Culture cells

• Run Western blots

• Conduct fluorescence microscopy

In this example, all the items in the bulleted list start with verbs, so the list runs parallel.

For option 2, you can remove the verb from the second bullet point and revise the introductory text to present the list more clearly.

Example 2.3

In the laboratory, students will learn the following techniques:

• Cell culture

• Western blotting

• Fluorescence microscopy

In this example, all the items in the bulleted list do not have verbs, so the list runs parallel.

Verb Forms in Sentences

Verb forms can also affect whether a bulleted list runs parallel.

Example 4.1

To infect cells, HIV adheres to a host cell and fused with the cell membrane, delivering the viral core into the cytoplasm.

In this list, the verbs are in the present tense (adheres), past tense (fused), and present participle (delivering). This variation in verb forms is more difficult for readers to understand.

To make the sentence clearer, you want to ensure that all verbs have the same form.

Example 4.2

To infect cells, HIV adheres to a host cell, fuses with the cell membrane, and delivers the viral core into the cytoplasm. 

This sentence is clearer and easier for readers to understand. 

Verb Forms in Bullets

Verb forms can also go awry in bulleted lists.

Example 3.1

Patients with traumatic brain injury were less likely to:

• Receive care that followed guidelines

• Underwent timely brain imaging

• Monitoring for arrhythmia

• Administration of preventive medications        

In this example, the first three items start with verbs in different tenses (receive, underwent, and monitoring), and the fourth item starts with a nominalization derived from a verb (administration of). These different formats will confuse readers.

To make the list clearer, you could change all items so that they have verbs in the same tense. However, in this case, the items in the list could share the same verb (receive).

Example 3.2

Patients with traumatic brain injury were less likely to receive:

• care that followed guidelines,

• timely brain imaging,

• monitoring for arrhythmia, and

• preventive medications.

This revision is easier for readers to read and understand.

Order of Information

When you need to tell readers more than one thing in a sentence, you want to ensure that the order of information runs parallel.

Consider the following example:

Example 5.1

Protein expression was measured with Western blotting, and RT-PCR was used to assess mRNA levels.

In this sentence, the first clause starts with a characteristic (protein expression) and ends with a technique (Western blotting). And the second clause starts with a technique (RT-PCR) and ends with a characteristic (mRNA levels). These two clauses present information in the opposite order. 

Protein expression (characteristic) —— Western blotting (technique)

RT-PCR (technique) —— mRNA levels (characteristic)

To make this sentence clearer, you can reverse the order of information in one of the clauses so that both clauses follow the same pattern.

Protein expression (characteristic) —— Western blotting (technique)

mRNA levels (characteristic) —— RT-PCR (technique)

With this revised order, you get a clearer version of this sentence.

Example 5.2

Protein expression was measured with Western blotting, and mRNA levels were assessed with RT-PCR. 

For this example, you might be tempted to condense this sentence by using the term respectively.

Example 5.3

Protein and mRNA expression were measured with Western blotting and RT-PCR, respectively.

Although this sentence might seem more concise, this phrasing forces readers to mentally assess which characteristic corresponds to which technique. Readers may even need to read the sentence again to connect the information. This backtracking violates the number one principle of making the reader's job easy. To make your content clearer, avoid using the term respectively in your writing. And if you are struggling with word count, there are many other ways to cut words from your writing.

Tips for Finding Parallel Structure

Parallel structure creates a pattern that makes information easier for readers to understand and remember. To assess parallel patterns in your writing, try the following strategies:

• Use the “Find” feature in your writing software to search for conjunction words (e.g., and, or) and colons. Check all items in the list to see if they run parallel.

• If you have a long list, or each item is a longer phrase, stack the items in separate lines (similar to a bulleted list). This format may reveal an unparallel structure in your list.

• Read a sentence out loud (or use the “Read Aloud” feature in your writing software). Pay attention to the sounds and notice when you hear something break the rhythm or repetition.