What exactly is a parallel structure?

When presenting any list or series in your writing, you should always strive for parallel structure. Parallel structure makes your words and ideas flow better. On the flip side, when you don't follow parallel structure, your sentences can be jarring and disjointed to the reader, which makes your ideas harder to follow.

Parallel structure means that items in a list are grammatically equivalent. That is, all the items in the list are gerunds (nouns ending in -ing), infinitive phrases (to be), past participles (verbs often ending in -ed), complete clauses, or any other parts of speech..

In the following table, the sentences on the left do not follow parallel structure, whereas the sentence on the right recast the sentence using parallel structure.

When he goes to the gym, David likes running, to play racquetball, and lift weights.

When he goes to the gym, David likes running, playing racquetball, and lifting weights.

Or...

When he goes to the gym, David likes to run, play racquetball, and lift weights.

Every day, Stephen wears blue jeans, white socks, and puts on his running shoes.

Every day, Stephen wears blue jeans, white socks, and running shoes.

On our trip to the country, Dianne said we would watch a polo match, we would have a picnic, and could sample apple cider at a farm.

On our trip to the country, Dianne said we would watch a polo match, we would have a picnic, and we would sample apple cider at a farm.

Or . . .

On our trip to the country, Dianne said we would watch a polo match, have a picnic, and sample apple cider at a farm.

People like Alexa because she smiles often, talks to everyone, and her desire to help people is high.

People like Alexa because she smiles often, talks to everyone, and helps people whenever she can.

Austin likes his apartment because of its spacious floorplan, it has bay windows, and it's within walking distance to downtown.

Austin likes his apartment because of its spacious floorplan, bay windows, and convenient location.