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.

ExclamationPoint The students’ objections were the injustice of the measures and that they were unconstitutional.

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 more logical and readily understandable if it were rewritten. The sentence below contains a verb instead of the nominalisation objections and then has a verb clause that contains a list of two elements, both of which are adjectives.

Small_OK The students objected that the measures were unjust and unconstitutional.

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 the example below, the list has three elements: the first two are noun phrases while the last one is a verb clause. Therefore, not

ExclamationPoint The master’s students will acquire the personality, the contacts and have the knowledge to succeed in almost any business venture.

but

Small_OK The master’s students will acquire the personality, the contacts and the knowledge to succeed in almost any business venture.

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

ExclamationPoint The Erasmus students will talk of their experiences in Paris, in Athens and Moscow.

but

Small_OK The Erasmus students will talk of their experiences in Paris, Athens and Moscow.

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

ExclamationPoint Students must
a) present the official application form,
b) their personal academic certificate,
c) and proof of payment.

but

Small_OK Students must present
a) the official application form,
b) their personal academic certificate,
c) proof of payment.

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

ExclamationPoint Master’s degrees not only prepare professionals but also researchers.

but

Small_OK Master’s degrees prepare not only professionals but also researchers.

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