Parallel phrases

Parallel structure should be used to balance a series of phrases with the same grammatical structure.

For example, avoid mixing noun phrases with verb phrases.

Not parallel

Initial trials showed that exposure to the chemical caused memory problems, intermittent dizziness, and deters sleep.

Parallel

Initial trials showed that exposure to the chemical caused memory problems, intermittent dizziness, and insomnia.

As with a series of verbs, a series of verb phrases should use parallel forms. Do not mix phrases based on an infinitive with phrases based on -ing verbs.

Not parallel

Her main duties were answering phone calls, filing records, and to conduct visitor surveys.

Parallel

Her main duties were answering phone calls, filing records, and conducting visitor surveys.