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Parallel structures

This section explains how you can use parallel grammatical structures in your writing. Parallel structures are important since they help readers process a text. Content draws on Bottomley (2021).

What is a parallel structure?

By parallel structures, we mean that two or more similar things in the text have the same grammatical form. Examples (1)–(6), from published engineering papers and student texts, show some examples. Parallel words and phrases are in bold.


In this work, we proposed a methodology with the aim of studying EIM in terms of its biophysical mechanism through FEA, and developing a simple circuit-based model which accurately emulates the tissues and effects of parametric changes of subcutaneous fat and muscle thickness. 

(Schrunder et al, 2021)

In example (1), the parallel -ing forms highlight the two aims of the study.

In example (2), there are several parallel structures. There is a list in the first sentence in the form of a, b + c, with each element comprising a noun phrase, starting with their. The second sentence has two parallel verbs in the present tense and with a third person ‘s’ ending. The third sentence has another list of three nouns, this time announced by a colon. 


Evolutionary optimization algorithms are widely adopted due to their structural simplicity, their complete non-use of derivatives for the cost evaluations and their ability to escape local minima. […] Specifically, they are based on a population approach, in which the solution of every iteration (called "generation") consists of multiple individuals and evolves to a selection of better-fit population members in the next generation. Their algorithm comprises the following key genetic phases: selection, crossover and mutation.

(Bitsi and Bosga, 2022)

In example (3), there is another list, with four noun phrases (design, analysis, simulation, and management software) modifying the main noun tools, this time with an Oxford comma before the final item: a, b, and c. There are then two parallel adjectives (home grown and commercial off the shelf).


System engineering projects typically involve the use of a variety of design, analysis, simulation, and management software tools that are home grown or commercial off the shelf (COTS).

(Chow, 1988)

Why is parallelism important?

Parallel structures are carefully balanced organisational structures based on repetition and contrast. The text changes in small increments, whilst retaining invariant elements. Repetition of certain known or assumed, or purely grammatical, elements gives focus to new, important or contrasting information.

Repetition is an important element of cohesion in texts. It has been suggested that repetition reduces the amount of processing required by the reader so that they are “freer to attend to the overall message” (Tyler, 1994: 686). In parallel structures, which have these repetitive elements, the reader is led to focus on the information that is new, important or contrasting.

Parallel structures in lists

Bulleted or numbered lists are a very effective way to make a text reader-friendly. The symmetry down the left-hand margin is a great aid to readability as the eye moves down the page. However, make sure your lists are parallel, that is, that each item on the list has the same grammatical form. The items in (4a) are not parallel, since they have different grammatical forms: nouns, imperative verbs, a full sentence, and -ing forms. This mix of forms makes the list harder for the reader to process. In (4b), the writer has used nouns throughout (in bold).

Note how the list is introduced with a colon. Read more about colons vs. semicolons here.  

(4a) Not parallel

The study comprises the following six phases:

  1. Synthesis study
  2. SWOT analysis
  3. Define the goal of the urban design guide
  4. Design process
  5. The urban design principles are formed.
  6. Implementing and monitoring

(4b) Parallel

The study comprises the following six phases:

  1. Synthesis study
  2. SWOT analysis
  3. Definition of the goal of the urban design guide
  4. Design process
  5. Formation of urban design principles
  6. Implementation and monitoring

Be careful to avoid 'false parallelism'

Be careful to avoid ‘false parallelism’, i.e. when items in a list might, at the first glance, seem to share the same grammar, but in fact don’t. For instance, in example (5a), transport and construction are nouns whereas biomedical is an adjective. In (5b), the adjective has been replaced by a third noun, biomedicine.

Not parallel:

(5a) Composite materials are widely used in a variety of applications in, for example, transport, construction, and biomedical.


(5b) Composite materials are widely used in a variety of applications in, for example, transport, construction and biomedicine.

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Bottomley, J. (2021) Academic Writing for International Students of Science. 2nd Edition. Routledge.

Tyler, A. (1994) The role of repetition in perceptions of discourse coherence. Journal of Pragmatics, 21, pp 671-688.


Schrunder, A. F., Rodriguez, S. & Rusu, A. (2022). A finite element analysis and circuit modelling methodology for studying electrical impedance myography of human limbs. IEEE Transactions on Bio-medical Engineering, 69(1), 244–255. https://doi.org/10.1109/TBME.2021.3091884.

Bitsi, K. & Bosga, S. G. (2022). A comparative study of IPM and WICSC machines for heavy vehicle application. 2022 International Conference on Electrical Machines (ICEM), Valencia, Spain, 2022, 14–20, https://doi.org/10.1109/ICEM51905.2022.9910942.

Chow, E. Y. (1988). Integrating system engineering software tools. IEEE Aerospace and Electronic Systems Magazine, vol. 13(11), 3–6, doi: https://doi.org/10.1109/62.730604.