parallel structure means using the same pattern of words to give equal weight to two or more ideas.
examples: correct: at summer camp, i like to hike, swim, and play tennis. incorrect: at summer camp, i like to hike, swim, and playing tennis. correct: percival lowell, who discovered the erstwhile planet pluto, used both his advanced understanding of mathematics and his background in astronomy to back up his hypothesis. incorrect: percival lowell, who discovered the erstwhile planet pluto, used both his advanced understanding of mathematics and he had a background in astronomy to back up his hypothesis.