If two or more ideas are parallel, they should be expressed in parallel grammatical form. Single words should be balanced with single words, phrases with phrases, clauses with clauses.
Parallelism makes form follow meaning.
Rule Description Example Balance parallel ideas in a series Readers expect items in a series to appear in parallel grammatical form. When one or more of the items violates readers' expectations, a sentence will be needlessly awkward. Sam is responsible for stocking merchandise, writing orders for delivery, and sales of computers. Sam is responsible for stocking merchandise, writing orders for delivery, and selling computers. Balance parallel ideas presented in pairs When pairing ideas, underscore their connection by expressing them in similar grammatical form.