Parallel structure is a way of writing that follows a pattern to demonstrate that all ideas have the same level of importance. For example, the following sentence is in parallel structure:
- The dog likes running, jumping, and swimming.
This is parallel structure because all of the verbs are in the present participle /gerund form (-ing) and all apply to the sentence starter "The dog likes..."
Another example of parallel structure is: The dog likes to run, jump, and swim. Once again, all the verbs in the sentence have the same structure and apply to the beginning of the sentence.
If we were to mix forms of the verb, such as "The dog likes to run, jump, and swimming", this would not be parallel structure because "run, jump, and swimming" are not all the same form.