1. Source: The Penguin Handbook (2d ed)
Parallelism
Source: The Penguin Handbook (2d ed)

2. Source: The Penguin Handbook (2d ed)
The principle of putting similar elements or ideas in similar grammatical form.
Source: The Penguin Handbook (2d ed)

3. Source: The Penguin Handbook (2d ed)
In the following passage describing old beliefs, anthropologist Margaret Mead presents similar information in parallel grammatical form:
Actually, almost every day, even in the most sophisticated home, something is likely to happen that evokes the memory of some old folk belief. The salt spills. A knife falls to the floor. Your nose tickles. Then perhaps, with a slightly embarrassed smile, the person who spilled the salt tosses a pinch over his left shoulder. Or someone recites the old rhyme, “Knife falls, gentleman calls.” Or as you rub your nose you think “That means a letter. I wonder who’s writing?”
--Margaret Mead, “New Superstitions for Old”
Source: The Penguin Handbook (2d ed)

4. Faulty Parallelism is Easier to See in a List
Parallel ideas Faulty parallelism
salt spills salt spills
knife falls knife falls
nose tickles nose tickles
person tosses person tossed
someone recites someone recites
Source: The Penguin Handbook (2d ed)

5. Balance Parallel Ideas
If two or more ideas are parallel, they are easier to grasp when expressed in parallel grammatical form. Single words should be balanced with single words, phrases with phrases, clauses with clauses.
Source: The Penguin Handbook (2d ed)

6. Source: The Penguin Handbook (2d ed)
Single Words
A kiss can be a comma, a question mark, or an exclamation point.
Source: The Penguin Handbook (2d ed)

7. Source: The Penguin Handbook (2d ed)
Clauses
This novel is not to be tossed lightly aside, but to be hurled with great force.
Source: The Penguin Handbook (2d ed)

8. Source: The Penguin Handbook (2d ed)
Phrases
In matters of principle, stand like a rock; In matters of taste, swim with the current.
Source: The Penguin Handbook (2d ed)

9. Balance Parallel Ideas
Readers expect items in a series to appear in parallel grammatical form. When one or more of the items violate readers’ expectations, a sentence will be needlessly awkward.
Source: The Penguin Handbook (2d ed)

10. Faulty Parallel Structure
Abused children commonly exhibit one or more of the following symptoms: withdrawal, rebelliousness, restlessness, and they are depressed.
Source: The Penguin Handbook (2d ed)

11. Faulty Parallel Structure
Hooked on romance novels, I learned that there is nothing more important than being rich, looking good, and to have a good time.
Source: The Penguin Handbook (2d ed)

12. Faulty Parallel Structure
After assuring us that he was sober, Sam drove down the middle of the road, ran one red light, and two stop signs.
Source: The Penguin Handbook (2d ed)

13. Writing About Men and Women
Biased/Faulty Parallelism
Joshua Baines and his wife
Men and girls
Rita Rando and Mr. Rando
Man and wife
Source: The Penguin Handbook (2d ed)

14. Linked with Coordinating Conjunctions
(fanboys; for, and, nor, but, or, yet, so)
At Lincoln High School, vandalism can result in suspension or even being expelled from school.
Source: The Penguin Handbook (2d ed)

15. Linked with Coordinating Conjunctions
(fanboys; for, and, nor, but, or, yet, so)
Many states are reducing property taxes for home owners and extend financial aid in the form of tax credits to renters.
Source: The Penguin Handbook (2d ed)

16. Linked with Correlative Conjunctions
(Correlative Conjunctions come in pairs: either…or, neither…nor, not only…but also, both…and, whether…or.
Make sure that the grammatical structure following the second half of the pair is the same as that following the first half).
Source: The Penguin Handbook (2d ed)

17. Source: The Penguin Handbook (2d ed)
Faulty Parallelism
Thomas Edison was not only a prolific inventor but also was a successful entrepreneur.
Source: The Penguin Handbook (2d ed)

18. Source: The Penguin Handbook (2d ed)
Faulty Parallelism
I was advised either to change my flight or take the train.
Source: The Penguin Handbook (2d ed)

19. Source: The Penguin Handbook (2d ed)
Exercise on Parallelism
Activities on Wednesday afternoons include fishing trips, dance lessons, and computers.
Tony found that it was faster to ride his bike than driving into the city.
The streets were not only too steep but also were too narrow for anything other than pedestrian traffic.
More plants fail from improper watering than any other cause.
The winner of the gluttony contest swallowed six large pancakes, slurped down a cream pie, gobbled six waffles, and four pastries in front of the dumbfounded judges.
Source: The Penguin Handbook (2d ed)