Laurie E. Rozakis, Ph.D. on parallel structure:
“Parallel structure means putting ideas of the same rank in the same grammatical structure. Your writing and speech should have parallel words, phrases, and clauses. Parallel structure gives your writing many admirable strengths, including the following:
Parallel words share the same part of speech (such as nouns, adjectives, or verbs) and tense (if the parallel word are verbs).
- My date was obnoxious, loud, and cheap; no doubt he thought I was gorgeous, personable, and witty.
- We pleaded, begged, and prayed—to no avail.
Parallel phrases create an underlying rhythm in your speech and writing…
- “For taking away our Charters, abolishing our laws, and altering the Forms of our Government . . . ” (Declaration of Independence)
- “Now the trumpet summons us again—not as a call to bear arms, though arms we need—not as a call to battle, though embattled we are—but a call to bear the burden of a long twilight struggle…” (John F. Kennedy’s inauguration speech)
Parallel clauses can give your writing balance as well….
- “Let every nation know, whether it wishes us well or ill, that we shall pay any price, bear any burden, meet any hardship, support any friend, oppose any foe to assure the survival and success of liberty.” (John F. Kennedy’s inauguration speech)
- “Our chiefs are killed; Looking-Glass is dead; Ta-Hool-Shute is dead.” (Chief Joseph’s surrender speech, 1877)”
Rozakis‘s book, The Complete Idiot’s Guide to Grammar and Style, is an excellent resource for writers of all kinds. You can find it here.