In mathematics, two lines are parallel if they never meet, like these:
In business writing, a parallel sentence is one where each part follows the same structure. Let's see an example.
Jane's skillset includes organizing large events, dealing with suppliers and ensuring customer satisfaction.
The main verb in our example sentence is includes. Three things are matched to this verb. If we express the sentence in bullet points, it may be clearer:
Note how each of these three points are written in the same way, using an -ing form. This is called parallel structure.
What about if we write the sentence in another way?
Jane is able to organize large events, deal with suppliers and ensure customer satisfaction.
Notice that the three points are now written using the base form of the verb, in order to match the phrase is able to:
This is also a parallel structure.
Now, what if we mix the two structures together:
Jane is able to organize large events, dealing with suppliers and ensuring customer satisfaction.
This sentence is NOT a parallel structure. As a result, it doesn't flow smoothly and, in fact, it is not grammatically correct.
Let's look at more examples:
Incorrect: We seek a candidate who is honest, capable and integrity.
Because integrity is a noun and honest and capable are adjectives, the sentence is not parallel. It is also not grammatically correct since we cannot say: 'a candidate who is integrity'. It should be 'a candidate who has integrity'.
We could rewrite the sentence like this:
We seek a candidate who is honest, capable and has integrity.
Now the sentence is grammatically correct, but it still is not parallel. How about this:
We seek an honest and capable candidate who has integrity.
The first sentence is grammatically correct, but the second sentence sounds better because it is parallel.
In the first sentence, the two parts of the subject are not in parallel. We can fix this in two ways, as illustrated in the next two sentences.
Make sure that you use OR for negative parallel expressions: