Parallelism in a sentence requires that similar ideas and elements be presented in similar forms (Figure 1). Parallelism is an important principle of both grammar and style; it helps promote balance, emphasis, clarity, and readability. Similarly, paragraphs should be focused on a single main idea or topic (i.e., unity), and transitions between sentences and paragraphs should be smooth and logical. Repeating key words can contribute to unity in and between sentences and paragraphs within an essay. A poorly organized paper rambles, drifting among unrelated topics in a haphazard and confusing fashion. How do you know if particular parts of a sentence need to be parallel to each other? Often, we know by spotting words that link or contrast items, such as and, or, and but.
Examples of Parallelism
Here are a few examples of parallelism:
- Nonparallel: Students spend their time going to classes, studying, working, and they wish they had time for a social life.
- Parallel: Students spend their time going to classes, studying, working, and wishing for a social life.
- Nonparallel: By the end of the quarter they're exhausted, irritable, but have learned a lot.
- Parallel: By the end of the quarter they're exhausted, irritable, but smarter.
- Nonparallel: High-school students hope for short school days, or four-day weeks would be great, too.
- Parallel: High-school students hope for short school days or four-day weeks.
Parallelism requires that an article (a, an, or the) or a preposition applying to all members of a series must either appear before the first item only or be repeated before each item. Here are a few examples of the rule in action:
- Nonparallel: We can pay with a mark, a yen, buck, or pound.
- Parallel: We can pay with a mark, a yen, a buck, or a pound.
- Nonparallel: I went to the store on Monday, Wednesday, and on Friday.
- Parallel: I went to the store on Monday, Wednesday, and Friday.
Some words require that certain prepositions precede them. When such words appear in parallel structure, it is important to include all of the appropriate prepositions, since the first one may not apply to the whole series of items. Here are a few examples of the rule in action:
- Nonparallel: His speech was marked by disagreement and scorn for his opponent's position.
- Parallel: His speech was marked by disagreement with and scorn for his opponent's position.
- Nonparallel: This is a time not for words but action.
- Parallel: This is a time not for words but for action.
Sentences with correlative expressions (both / and; not / but; not only / but also; either / or; first, second, third) should employ parallel structure as well. Simple rewriting can often remedy errors in these types of sentences. Here are a few examples of the rule in action:
- Nonparallel: Either you must grant her request or incur her ill will.
- Parallel: You must either grant her request or incur her ill will.
- Nonparallel: My objections are first, the injustice of the measure, and second, that it is unconstitutional.
- Parallel: My objections are first, that the measure is unjust, and second, that it is unconstitutional.
In some instances, you must figure out which grammatical structures are logically parallel before making them structurally parallel. Here is an example:
- Correct: Sal applied himself in his new job, arriving early every day, skipping lunch regularly, and leaving late every night.
In the sentence above, the –ing participle phrases (arriving early every day, skipping lunch regularly, and leaving late every night) are parallel. The main clause—applied himself in his newjob—is not parallel to these participle phrases. This is correct because the main verb is applied, and the –ing phrases provide additional information about how Sal applied himself. It would distort the meaning to change the sentence to this superficially parallel version:
- Incorrect: Sal applied himself in his new job, arrived early every day, skipped lunch regularly, and left late every night.
This version gives all the activities equal emphasis, instead of making the last three activities subordinate to the main activity (applied himself in his new job).