Words or Phrases in a Series (Parallelism)

Phrases in a series need to be in the same form in order to make sense easily in a sentence. That is, if you have a series of coordinate (equally important) phrases in a sentence, you need to put them into the same grammatical form (all '-ing' words, all past tense, all starting with nouns, etc.).The form itself doesn't matter; the consistency does.

Example:

Incorrect: Henry James Sr. liked reading and writing philosophy, discussing his ideas with his sons William and Henry, and to offer opportunities to his children to pursue whatever interests they developed. (Most phrases start with -ing words, so "to offer" should be changed to "offering" to make sense.)

Correct: Henry James Sr. liked reading and writing philosophy, discussing his ideas with his sons William and Henry, and offerring opportunities to his children to pursue whatever interests they developed.

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Incorrect: William James was a famous psychologist, writer, philosopher, and belonged to the illustrious James family; he was a not-so-famous artist. (Most phrases start with nouns, so "belonged to the... family" should be changed to "member of the... family" to make sense.)

Correct: William James was a famous psychologist, writer, philosopher and member of the illustrious James family; he also was a not-so-famous artist.

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Incorrect: Henry James Jr., William's brother, wrote many short stories and novels, becomes part of the English literary scene, although he was an American, and completing a major revision of his already published works toward the end of his life. (The first phrase starts with a past-tense verb, "wrote," so the rest of the phrases should start with past tense verbs such as "became" and "completed.")

Coorect: Henry James Jr., William's brother, wrote many short stories and novels, became part of the English literary scene (although he was American) and completed a major revision of his already published works toward the end of his life.

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Incorrect: Alice James, William and Henry's sister, experienced a life in her father's and siblings' shadows, consulted numerous doctors about her nerves, had a series of breakdowns and never fully realizes a life of her own. (All of the phrases use past- tense verbs except the last, so "realizes" should be changed to "realized.")

Correct: Alice James, William's and Henry's sister, experienced a life in her father's and siblings' shadows, consulted numerous doctors about her nerves, had a series of breakdowns, and never fully realized a life of her own.