The below sentence was given as an example in chapter 12, of the SC GMAT Strategy Guide.

"At current prices, oil in the Antarctic may be worth drilling for, if wells can be dug there and environmental concern addressed."

Unable to understand how parallelism is brought by using AND, because environmental is a adjective and wells is a noun. "environmental concern addressed." where is auxiliary verb

  • 2
    Because the clauses "wells can be dug there" and "environmental clauses can be addressed" are parallel and joined by "and" the phrase "can be" does not have to be repeated. Indeed it is arguably better style to omit it from the second clause and let it be implied. Does that explain what has happened to the auxiliary verb in "environmental clauses be addressed"?
    – BoldBen
    Commented Sep 2, 2020 at 7:01
  • 1
    To this native speaker the parallelism seems quite trivial and natural if I just let it wash over me. But if I go back and try to analyse the exact construction it suddently looks quite complex, because of the way it deletes two completely different potentially repeated elements (if, can be). Commented Sep 2, 2020 at 11:32
  • ... the deletion masks a zeugma. The Mask of Zeugma? But it hybridises meaning too. I'd expect 'if we can get the prospective industrialists to contract to properly address environmental issues.' Perhaps an [irrealis] 'be' rather than 'can be' deletion. // I agree; this is suboptimal. Commented Sep 2, 2020 at 11:53
  • "where is auxiliary verb?" Auxiliary verb has been deleted by Conjunction Reduction. Commented Sep 2, 2020 at 13:59

3 Answers 3


At current prices, oil in the Antarctic may be worth drilling for, if [wells can be dug there] and [environmental concerns ___ addressed].

The sentence contains what is known as 'gapped coordination', where the middle part of the second coordinate is missing but recoverable from the corresponding part of first coordinate.

The gap, marked '____' , is understood by reference to the first coordinate; in this case "can be".

The fact that gapping is appropriate here demonstrates that the coordinates have parallel structures.


To quote this article on Grammarly, parallelism in grammar is like parallelism in geometry: they face the same direction and never meet. So the clause "if wells can be dug there" and "[if] environmental concern addressed" are two sentences which both relate to "oil in Antarctica may be worth drilling for", but do not have much in common on their own.

As for the auxiliary verbs, here is a list of auxiliary verbs in English. Maybe you can clarify what the purpose of this exercise was, and where you had to find the auxiliary verb.

  • 2
    The important factor is that the two coordinates are clauses, each serving as complement of the preposition "if": if [wells can be dug there] [and environmental concern addressed].
    – BillJ
    Commented Sep 2, 2020 at 6:20
  • @BillJ yes exactly, thanks for the addition!
    – Cyhiraeth
    Commented Sep 2, 2020 at 6:59

You say you do not understand "because "environmental" is a[n] adjective and "wells" is a noun"; you have to understand that parallelism bears upon clause structure and that the units that make up the clauses must show a certain uniformity (parallelism); the following are items of importance in this subject (agreement and parallelism).

  • Verb Forms - Olympic athletes usually like practicing, competing, and to eat ice cream sandwiches. (wrong)

  • Nouns vs. Verbs - For dinner we like lamb chops and to fry brussel sprouts. (wrong)

  • Use of articles - Parallelism requires that an article (a, an, or the) or a preposition applying to all items in a list either appear before the first item only or be repeated before each item. Here is an example of the rule:

    Nonparallel: We can pay with a mark, a yen, buck, or pound.

  • adverb and prepositional phrase - The detective deftly and with pizzazz outlined how the crime had been committed. (wrong)

However, this principle is not applied to the extent that you envisage: one of the noun phrases can comprise no adjective while another does so; the principle of parallelism would otherwisebe too restrictive.

  • Athletes like long vacations, travel and frequent competitions.

  • (wrong) Athletes like long vacations, travel and to compete frequently.

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