Faulty Parallelism
Written by Jerry Plotnick, University College Writing Centre   

What is faulty parallelism?

Look out for faulty parallelism whenever you use one of the following constructions:

a and b
a, b, and c
a or b
a, b, or c
not only a but also b

The clauses or phrases joined by the conjunctions should have similar grammatical structures to ensure that your reader can follow the logic of your sentence and to avoid awkwardness. Consider the sentence,

My first-year philosophy professor was informative, lively, and a source of inspiration.

Notice that the first two phrases in the a, b, and c construction are adjectives, while the third is a noun phrase. This sentence suffers from faulty parallelism.

How to identify and repair faulty parallelism

To check whether the elements of a construction are in parallel, place boxes around them. Next, label the boxes.

My first-year philosophy professor was informativea, livelyb, and a source of inspirationc.

To repair the faulty parallelism here, you will have to change the elements a and b into noun phrases or the element c into an adjective. Always choose the simplest option. In this case it is easiest to change the final element, c, into an adjective:

My first-year philosophy professor was informativea, livelyb, and inspiringc.

Often faulty parallelism can be repaired by paying close attention to where you place your verbs. The faulty parallelism in the following sentence is easy to detect once you place boxes around the two elements of the not only but also construction:

My philosophy professor not only demonstrated how to reason persuasivelya but also how to avoid logical fallaciesb.

Note that element a begins with a verb but element b doesn't. To repair the faulty parallelism, you can add a verb to the start of element b. However, since the same verb will work for both parts of the construction, the more elegant solution is to drag the verb demonstrated to the front of the whole construction:

My philosophy professor demonstrated not only how to reason persuasivelya but also how to avoid logical fallaciesb.

Problems with parallelism often arise from the careless use of clauses beginning with the subordinating conjunction that:

He warned me to revise my essaya and that I should pay close attention to parallel structuresb.

To repair the problem, choose either an infinitive (to + verb) or a that clause on both sides of the a and b construction. In this example, the infinitive provides the more elegant solution:

He warned me to revise my essaya and to pay close attention to parallel structuresb.

 

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