1. Parallel Structure
Parallel structure means using the same pattern of words to show that two or more ideas have the same level of importance.
This can happen at the word, phrase, or clause level. The usual way to join parallel structures is with the use of coordinating conjunctions such as "and" or "or."

2. She is probably going to fail the exam.
Parallelism is a useful way of making a sentence or a text cohesive by using similar grammar .
For ex., we can use the same tense or aspect, similar word order, or repeat a particular grammatical form.
In a text:
She is probably going to fail the exam.
And she is probably going to blame her teacher.

3. We AVOID sudden changes in grammar as this can make a written text difficult to understand:
I can’t wait to lie on the sand. Swimming in the sea is great. To sunbathe is something I would love to do as well.
I can’t wait to be lying on the sand, sunbathing and swimming in the sea.

4. Understand the problem.
For a list of actions or items, you must maintain parallel structure.
To do this, use equal grammatical units.
If the first item is a noun, then the following items must also be nouns; if the first item is a verb, then make the other items verbs as well.

5. Nonparallel structure looks like this:
At the garden store,
Larissa bought , and
Parallel structure looks like this:
At the garden store,
Larissa bought , and
At the garden store,
Larissa bought , and

6. This is an example of non-parallel structure.
At the garden store, Larissa bought plastic pink flamingos, ceramic gnomes, and then she impulsively added a concrete mermaid to her cart.
This is an example of non-parallel structure.
At the garden store,
Larissa bought , and

7. Now compare:
At the garden store, Larissa bought plastic pink flamingos, ceramic gnomes, and a concrete mermaid.
At the garden store, Larissa bought plastic pink flamingos, rescued ceramic gnomes from the sale bin, and impulsively added a concrete mermaid to her cart.

8. Parallel Words and Phrases
With the -ing form (gerund) of
words:
Mary likes hiking, swimming, and bicycling.
With infinitive phrases:
Mary likes to hike, to swim, and to ride a bicycle or Mary likes to hike, swim, and ride a bicycle.
(Note: You can use "to" before all the verbs in a sentence or only before the first one.)

9. Do not mix forms. Not Parallel: Parallel:
Mary likes hiking, swimming, and to ride a bicycle.
Parallel:
Mary likes hiking, swimming, and riding a bicycle.

10. Not Parallel:
The production manager was asked to write his report quickly, accurately, and in a detailed manner.
Parallel:
The production manager was asked to write his report quickly, accurately, and thoroughly.

11. Not Parallel: The teacher said that he was a poor student because he waited until the last minute to study for the exam, completed his homework in a careless manner, and his motivation was low.
Parallel: The teacher said that he was a poor student because he waited until the last minute to study for the exam, completed his homework in a careless manner, and lacked motivation.

12. A parallel structure that begins with clauses must keep on with
Changing to another pattern or changing the voice of the verb (from active to passive or vice versa) will break the parallelism.

13. Example :
Not Parallel:
The coach told the players that they should get a lot of sleep, that they should not eat too much, and to do some warm-up exercises before the game.

14. Parallel:
The coach told the players that they should get a lot of sleep, that they should not eat too much, and that they should do some warm-up exercises before the game.
OR:
The coach told the players that they should get a lot of sleep, not eat too much, and do some warm-up exercises before the game.

15. The salesman expected that he would present his product at the meeting, that there would be time for him to show his slide presentation, and that questions would be asked by prospective buyers.
The salesman expected that he would present his product at the meeting, that there would be time for him to show his slide presentation, and that prospective buyers would ask him questions.
NOT
PARALLEL:
Active,
then
Passive:
PARALLEL:
Active

16. Be sure to keep all the elements
Lists After a Colon :
Be sure to keep all the elements
in a list in the same form.
Not Parallel: The dictionary can be used for these purposes: to find word meanings, pronunciations, correct spellings, and looking up irregular verbs.
Parallel: The dictionary can be used for these purposes: to find word meanings, pronunciations, correct spellings, and irregular verbs.

17. Know the solution.
Once you discover a nonparallel item, you have two options:
you can make it conform to the other grammatical items in the sentence
you can alter the other items to establish parallel structure.

18. Look at this example:
We spent the hour in the waiting room reading old magazines, eating stale cookies from the vending machine, and we wiggled on the hard plastic chairs.
Reading old magazines and eating stale cookies are participle phrases; we wiggled ..., however, is a main clause.

19. If we fix the nonparallel item,
the sentence looks like this:
We spent the hour in the waiting room reading old magazines, eating stale cookies from the vending machine, and wiggling on the hard plastic chairs.

20. If we alter the first two items,
then the sentence looks like this:
In the waiting room, we read old magazines, ate stale cookies from the vending machine, and wiggled on the hard plastic chairs.

21. Not only ... but also, either ... or, and neither ... nor
Recognize these special cases:
Not only ... but also, either ... or, and neither ... nor
all require special attention when you are proofreading for parallelism.
These correlative conjunctions require equal grammatical units after both parts of the conjunction. You can have two main clauses like this:

22. For a shorter sentence, use two prepositional phrases:
Not only did Jerome buy flowers for his mother, but he also purchased a bouquet for Yolanda, his wife.
For a shorter sentence, use two prepositional phrases:
Jerome bought flowers not only for his mother but also for Yolanda, his wife.
Or you can have two nouns as this version does:
Jerome bought flowers for not only his mother but also Yolanda, his wife.

23. Skim your paper, pausing at the words "and" and "or
Skim your paper, pausing at the words "and" and "or." Check on each side of these words to see whether the items joined are parallel. If not, make them parallel.
If you have several items in a list, put them in a column to see if they are parallel.
Listen to the sound of the items in a list or the items being compared.
Do you hear the same kinds of sounds? For example, is there a series of "-ing" words beginning each item? Do your hear a rhythm being repeated? If something is breaking that rhythm or repetition of sound, check to see if it needs to be made parallel.
Proofreading Strategies to Try: