Parallel structure means that the same pattern of words is repeated within a sentence or passage. It is a grammatical necessity within a sentence, but it can also be used as a rhetorical device to emphasize ideas.
Incorrect: Remember to buy lettuce, tomatoes, grapes, don’t forget cucumbers, milk, butter, and eggs are really important.
Correct: Remember to buy lettuce, tomatoes, grapes, cucumbers, milk, butter, and eggs.
This list uses parallel structure because every item is a noun.
Incorrect: The Global Goals for Sustainable Development aim to eliminate poverty, ending hunger, and good health and well-being.
This list is not parallel because the first item is an infinitive phrase (“to eliminate poverty”), the next is a gerund (“ending hunger”), and the last is a noun phrase (“good health and well-being…”).
Correct: World leaders share the goals of eliminating poverty, ending hunger, promoting good health and well-being, guaranteeing access to quality education, and mandating gender equality.
This list uses a parallel series of gerunds (-ing words).
Also Correct: World leaders came together to outline a set of global goals: no poverty, zero hunger, good health and well-being, quality education, etc.
This list uses a series of noun phrases.
Writers purposely create lists for emphasis, often to connect ideas or to bring attention to the abundance of the items listed. Here are two examples of parallel structure that draw attention to the many aims of the Global Goals for Sustainable Development.
The Global Goals for Sustainable Development will eliminate poverty; they will end hunger; they will promote good health and well-being; they will guarantee access to quality education.
This list uses a series of independent clauses with identical beginnings (“they will”). This repetition emphasizes each statement.
The Global Goals for Sustainable Development aim to eliminate poverty, to end hunger, to promote good health and well-being, and to guarantee access to quality education.
This list uses a series of infinitive phrases. The repetition of “to” emphasizes each item in the list.