Academic Writing for International Students of Science - Jane Bottomley 2015
5.3 Lists and parallel structures
5 Sentence structure 2
When two or more similar things are mentioned in a sentence, parallel structures, that is to say repetition of words, phrases and syntactic patterns (including punctuation), are often employed.
Multiple items are also often presented as lists. Items in a list should be balanced in terms of grammatical structure, i.e. they should be parallel structures.
These two devices, lists and parallel structures, when carefully constructed and punctuated, can greatly improve clarity and readability.
Find examples of lists and parallel structures in the sentences below. What do you notice about punctuation? Compare your ideas to the features listed in the Study Box that follows.
1) Some of the most unusual and versatile of all the mammals are the groups that live, feed and reproduce under water.
2) Epidemic outbreaks of disease are fostered by factors such as poor socioeconomic conditions, ignorance of the cause of infection, natural disasters, and poor hygiene.
3) In actively respiring tissues, where the concentration of carbon dioxide is high, haemoglobin readily releases its oxygen, while in the lungs, where blood carbon dioxide is low, haemoglobin readily binds oxygen.
4) A cancer that arises in epithelium is called a carcinoma; one that arises in connective tissue is called a sarcoma.
5) There are three basic types of water pollutants: toxic chemicals, biological materials and thermal discharges.
6) Optical astronomical telescopes fall into two main classes: refracting telescopes (or refractors), which use lenses to form the primary image, and reflecting telescopes (or reflectors), which use mirrors.
7) The cell cycle can be divided into four main stages: the M phase, which consists of mitosis (nuclear division) and cytokinesis (cytoplasmic division); the G1 phase, in which there is a high rate of biosynthesis and growth; the S phase, in which the DNA content of the cell doubles and the chromosomes replicate; the G2 phase, during which the final preparations for cell division are made.
Study Box: Punctuation in lists and parallel structures
1) Three simple items in a list should be written a, b and c, though a comma is often used before and, and can sometimes aid clarity if the items are long or contain another and within, e.g.
an equal balance of carbohydrates, fruit and vegetables, and protein
2) Precise, ’mirrored’ (i.e. the same punctuation used in each parallel item), use of commas can enhance the use of parallel structures and improve readability.
3) Semi-colons can also be used to enhance the link between parallel structures.
4) A colon can be used to introduce a list, especially if it is complex. The items in a list can be separated with commas if fairly short and simple; longer, more complex items should be separated by semi-colons. As you can see from 7, this type of structure can be extended to form a whole, single-sentence paragraph.
Chapter 9.7 for information on more detailed lists
Be careful to avoid ’false parallelism’, i.e. when items in a list do not share the same grammar, e.g.
Composite materials are widely used in a variety of applications in, for example, transport, construction, and biomedical.
Composite materials are widely used in a variety of applications in, for example, transport, construction and biomedicine.
Combine the notes below to form sentences. Use parallel structures where possible, and commas, colons and semi-colons where necessary. You will also need to form the verb correctly, add articles, etc., in order to form grammatical sentences.
1) rock — three types — igneous/sedimentary/metamorphic
2) blood vessels — three types — arteries (carry blood away from heart)/capillaries (connect arteries to veins)/veins (carry blood back to heart)
3) deciduous trees (lose their leaves seasonally)/evergreen trees (green foliage all year round)
4) taste — four types (according to western experts) — sweet/salty/sour/bitter — also umami (according to eastern experts)
5) trunk of a tree — three physical functions to perform — firstly must support crown — region responsible for production of food and seed — secondly must conduct mineral solutions absorbed by roots upwards to crown — thirdly must store manufactured food (carbohydrates) until required