Parallel Structure (Parallelism)
Parallelism means using the same pattern of words to show that two or more ideas have the same level of importance. This makes writing clear and easy to read.
The Rule
If you list items, they must all be the same grammatical form (all gerunds, all infinitives, all nouns, etc.).
Examples
Incorrect: I like hiking, swimming, and to ride a bicycle.
Correct (All Gerunds): I like hiking, swimming, and riding a bicycle.
Incorrect: The manager is responsible for writing reports, managing staff, and to answer emails.
Correct: The manager is responsible for writing reports, managing staff, and answering emails.