There are many instances in academic writing when your sentences will contain more than one idea. Often, this occurs in the form of a list when writing a thesis statement, but parallelism can appear in any type of sentence, not just theses.
Parallelism means taking ideas that are similar in content and making sure they are similar in form. In fact, the sentence I just wrote is parallel. Here’s that same sentence, but NOT parallel:
Parallelism means taking ideas that are similar in content and to make sure they are similar in form.
See what happened? The first sentence says Parallelism means taking … making, while the other says Parallelism means taking … to make. For these to be parallel, the forms need to match!
For an explanation and more examples of parallelism (as well as some tips on how to check for it), you can watch the video below.
(Examples sentences in video: https://www.thoughtco.com/editing-exercise-faulty-parallelism-1690963)