English Parallel structure

Parallel structure is the rule that items joined together should have the same grammatical form. When a sentence lists several things, or joins them with a conjunction like "and" or "or," each item should follow the same template.

When two verbs describe the same subject, they must match in tense and number. In "Bats are mobile and often congregate near roosts," both "are" and "congregate" are present tense and plural, matching the plural subject "bats." Writing "congregated" would break the parallel.

In a list or a paired phrase, keep every item in the same form. "The scientist works to supplement academic science and to bring traditional knowledge to it" keeps both phrases as "to + verb." Switching one to "bringing" would break the structure.

Punctuation also carries parallel structure. When each item in a list already contains a comma, use semicolons to separate the items themselves. In "I visited Japan, in 1995; Italy, in 1999; and the USA, in 2001," every item keeps the same "place, in year" form, and the semicolons make the boundary between items clear — without them, a reader could not tell where one item ends and the next begins.

To check, find the conjunction or the list, read the joined items one after another, and confirm they fit the same template and are separated consistently. If one item does not match, adjust it so it lines up with the others.

Which is correct: "The coach told the team to practice hard, to stay focused, and winning games," or with "to win games"?
Use "to win games." The three items must share the "to + verb" form, so "winning" breaks the parallel.

A sentence reads: "The new policy protects workers and _____ their benefits," where the first verb "protects" is present-tense singular. Should the blank be "expanded" or "expands"?
Use "expands." It must match the tense and number of "protects."

Which fits: "The lab studies climate, ecosystems, and how species migrate," or "climate, ecosystems, and migration"?
Use "migration." The list should be all nouns, so the clause "how species migrate" should become the noun "migration."

A sentence describes three trips, each with a place and a year: Japan in 1995, Italy in 1999, and the USA in 2001. How should the list be punctuated?
Because each item already contains a comma, separate the items with semicolons: "The team traveled to Japan, in 1995; to Italy, in 1999; and to the USA, in 2001." This keeps every item parallel and clearly separated.