An important principle in written English is that lists of two or more items must be grammatically parallel. That means they must be the same type of word, phrase, or clause. Writers most often need to use parallel form with coordinating conjunctions (such as and, or, but) and correlative conjunctions (either … or, neither … nor, not only … but also).

Write vertically!

Even advanced learners and native speakers of English sometimes struggle with parallel form in long sentences. One trick that can help is to write the items in a vertical list. This makes the grammatical patterns easier to see.

Example 1a: American language, regional culture, and to eat local food are difficult for some international students. (NOT PARALLEL)

American language

regional culture

and         to eat local food                are difficult for some international students.

Now you can see that language and culture are nouns, but to eat is an infinitive verb. To correct the sentence, change to eat to a non-verbal noun:

Example 1b (better) American language, regional culture, and local food are difficult for some international students. (PARALLEL).

In Example 2a, the writer has confused two different types of clause.

Example 2a: Many students like to meet new friends and experiencing campus life. (NOT PARALLEL)

Many students like          to meet new friends

                            and          experiencing campus life.

Although the verb like can be followed be an –ing verb or a to infinitive, in a list of two activities, they both need to use the same form.

Example 2b (better): Many students like meeting new friends and experiencing campus life. (PARALLEL)

The correlative structure not only … but also follows the same rules.

Example 3a: ESL classes teach not only the skills necessary for academic success but also understanding the culture. (NOT PARALLEL)

ESL classes teach              not only                 the skills necessary for academic success

                                               but also                 understanding the culture.

As you can now see, not only is followed by a noun phrase (with a reduced relative clause) while but also is followed by an –ing clause.

Example 3b (better): Classes teach not only the skills necessary for academic success but also cultural awareness. (PARALLEL)

Parallel structures help make writing clearer and more sophisticated. For more practice, download this handout of exercises.

 

Click here to download the “Parallel Form” attachment.