Parallelism, or parallel structure, refers to the balance achieved when sentence parts match in style, voice, tense, and context. Writers of all levels must pay careful attention to ensure their writing maintains parallel consistency and balance.
The simplest error in parallelism occurs when adjectives, nouns, or verbs do not remain alike within a sentence: I read books, watch films, and like to listen to music. While the first two clauses are similar, the third breaks the pattern. An improved version may read: I read books, watch films, and listen to music. In lists, verbs should agree with verbs, adjectives with adjectives, and nouns with nouns. If a list begins in simple present, it shouldn’t end in present participle: prefer I bike, run, and swim to I bike, run, and go swimming. When using prepositional phrases, repeat the preposition if it does not begin each phrase: government of the people, by the people, for the people.
When an auxiliary verb begins a verb phrase, maintain it throughout the list: prefer I like to go biking, swimming, and walking to I like to go biking, swimming, and take walks. (A weak writer may be tempted to correct the incorrect version as: I like to go biking, swimming, and on walks, which works grammatically, but is not parallel; the first two habits take the present participle while the last does not.)
Contextual parallelism may be harder to spot than grammatical parallelism: The strongman stands six feet tall, weighs three hundred pounds, and pulls a firetruck a hundred yards. Although grammatically correct, the sentence changes context after the conjunction. A potential fix, while not pretty, may read: The strongman stands six feet tall and weighs three hundred pounds, and he can pull a firetruck a hundred yards. Keep related clauses or sentences thematically similar to maintain contextual parallel structure.