Parallel Structure

Parallelism means that each item in a list or comparison is using the same pattern, which is used to show two or more ideas have the same level of importance in English writing. This can happen at the word, phrase, and clause level. If the first item in a list is a noun, all the following items should be written as nouns also; if the first item is a verb, all the others should be verbs. Example:

The growth of China’s mega cities will be driven by three factors-the geographical factor, neighboring cities merging and rural migration to cities.

This sentence is not parallel, since three listed factors are not in the same form.

The growth of China’s mega cities will be driven by three factors-the geographical factor, the merger of neighboring cities and rural migration to cities.

If the first item is a clause, the following items should keep on being in clauses. Example:

The coach told the players that they should get enough sleep, not to eat too much, and that some warm-up exercises should be done before the game.

Changing to another pattern or changing the voice of the verb, such as from active to passive, will break the parallelism.

The coach told the players that they should get enough sleep, that they should not eat too much, and that they should do some warm-up exercises before the game.

Parallel structure is very useful because it could make our sentences look orderly. The usual way to join parallel structures is with the use of coordinating conjunctions and paired conjunctions, such as “and”, “or”, “neither…nor”, and “not only…but also”. Example:

She can speak not only English but also French.


Practice exercise:
Improve the texts below by correcting all the non-parallel elements in the following paragraphs.

When learning any language, a good dictionary is an extremely valuable tool. However, like all tools, it is valuable only if it is used correctly and (1) efficient. In order to maximize the use of this language tool, learners need to not only understand but (2) have also to use the information that dictionaries can provide. A good dictionary provides more than correct spellings of words and (3) definitions that are precise. It also gives information about pronunciation, what part of speech a word is, etymology and (4) tells people how a word is used. Apart from this, a good dictionary informs the learner about whether a word is ‘informal’, ‘non-standard’, ‘archaic’ (5) and also provides labels like ‘slang’ when words cannot be used in formal contexts. Other kinds of information include synonyms, plural forms and the (6) dictionary also gives parts of irregular verbs. Learners should try to have the most current version of a dictionary so that even words that have recently entered the language will be included. Currency also ensures the inclusion of new meanings of old words. Language teachers sometimes discourage learners from buying bilingual dictionaries as these may be out of date, (7) the implication that words can be directly translated may be there and this may be inaccurate

Key:
(1) efficiently
(2) also to use
(3) precise definitions
(4) how a word is used
(5) and ‘slang’
(6) parts of irregular verbs
(7) or may imply that words can be directly translated

(From http://courses.nus.edu.sg/courseware/ITSELF/)