Parallelism refers to giving each element in a list the same grammatical category (noun phrases, verb clauses, infinitives, etc.). The similarity of the grammatical form makes it easier for readers to perceive a similarity in content and function. The sentence below is not parallel.



The first element of the list (the injustice of the measures) is a noun phrase while the second (they were unconstitutional) is a verb clause. The sentence would be clearer if it were rewritten. The sentence below contains a verb instead of the nominalization objections and then has a verb clause that contains a list of two elements, both of which are adjectives.



In any series of items, then, make sure that each element of the series is in exactly the same form as all of the others. In other words, don't follow the example below, where the writer tries to combine two noun phrases (the personality and the contacts) with a verb clause (have the knowledge).



Instead, rephrase the sentence like this:



This general guideline can affect even the smallest, and seemingly trivial, of words. Therefore, not



but



The principle of parallelism should also be respected in vertical lists. Therefore, not



but



Take particular care when you use such structures as not only ... but also. Therefore, not



but