5.2 Focus on punctuation - 5 Sentence structure 2

Academic Writing for International Students of Science - Jane Bottomley 2015

5.2 Focus on punctuation
5 Sentence structure 2

Punctuation in English can be viewed as stylistic or grammatical.

Stylistic punctuation can involve, for example, deciding between a full stop or a semicolon between two sentences. People have different preferences, and acceptable variation can be found across academic texts. However, these choices are still important because they can affect clarity and readability.

Grammatical punctuation is not a matter of choice because the punctuation here is intrinsically connected to the meaning, as we saw with relative clauses in 4.2.4.

Focussing on punctuation can help you to consolidate your understanding of sentence structure as a whole.

Good command of punctuation can help you achieve clarity and focus in your writing.

Explorative Task

Which of the pairs do you find easier to read or more effective? Why? Compare your ideas with the Study Box which follows.


a) In 1929 Alexander Fleming discovered penicillin.

b) In 1929, Alexander Fleming discovered penicillin.


a) St Thomas’ hospital concerned about the number of infections began to transfer patients to other centres.

b) St Thomas’ hospital, concerned about the number of infections, began to transfer patients to other centres.


a) Newton the great mathematician and physicist formulated three laws of motion.

b) Newton, the great mathematician and physicist, formulated three laws of motion.


a) The guidelines concerning the prevention of type 2 diabetes recommend plenty of exercise and they propose a diet based around protein, slow-release carbohydrates and fruit and vegetables.

b) The guidelines concerning the prevention of type 2 diabetes recommend plenty of exercise, and they propose a diet based around protein, slow-release carbohydrates, and fruit and vegetables.


a) If detected early enough the disease is treatable.

b) If detected early enough, the disease is treatable.


a) The disease is treatable if detected early enough.

b) The disease is treatable, if detected early enough.


a) Aristotle believed the world to be composed of four elements, earth, water, air and fire.

b) Aristotle believed the world to be composed of four elements: earth, water, air and fire.


a) Mammals are warm-blooded. Reptiles are cold-blooded.

b) Mammals are warm-blooded; reptiles are cold-blooded.

Study Box: Common punctuation patterns

Examples taken from:

Dawkins, R. (ed.) (2008) The Oxford Book of Modern Science Writing.


Commas are the equivalent of changing gear when driving; you come to a point where you need to slow down a little or turn a corner. The commas help you negotiate these changes, but also, and perhaps more importantly, they enable you to take your reader along with you.

Peck and Coyle (2012: 54)

Think of commas, therefore, as a way to guide (or drive!) your reader through the text.

1) It can make a sentence easier to follow for the reader if you separate words and phrases coming before (or sometimes after) a clause with a comma (see 1 above), especially in longer sentences, e.g.

From Pythagoras to string theory, the desire to comprehend nature has been framed by the Platonic ideal that the world is a reflection of some perfect mathematical form.

The comma serves to ’introduce’ the main point, thus guiding the reader.

Likewise, use commas if a word or phrase ’interrupts’ a clause or structure (see 2 above), e.g.

It is mathematics, more than anything else, that is responsible for the obscurity that surrounds the creative process of theoretical physics.

In this way, the reader is able to extract the main point easily.

This principle applies to phrases used in ’apposition’ (i.e. consecutive phrases, usually noun phrases, the second one defining or modifying the first — see 3 above), e.g.

Aristotle, the first great biologist, wrote that each sense organ ’receives the form of the other object without its matter’.

2) It is optional to use a comma before and/but/or to separate coordinate clauses (, but it can often help to make long sentences easier to read (see 4 above); when listing items, a comma can also help avoid confusion (see 4 above), e.g.

Parallel advances in biochemistry have provided us with detailed knowledge of how energy is converted to chemical bonds and chemical bonds to energy, and how the elementary components of living cells are synthesised.

3) Separate the main clause and subordinate clause with a comma when the subordinate clause comes first (see 5 above) (, e.g.

If we examine the process of DNA replication, we see that there are a number of basic requirements.

If the main clause comes first, it is not necessary to use a comma, although people often do, and it is considered acceptable if it makes sense. (In 6 above, the comma is unnecessary, but could be used to add emphasis; however, in general, avoid commas which are unnecessary as they can make the page too ’busy’ and difficult to read — like driving along a bumpy road!)

4) Use commas to separate non-defining relative clauses from the main clause ( 4.2.4), e.g.

Darwin regarded his work as a clear break with past biology, which believed in an instantaneous creation of an unchanging world whose various parts functioned together like so many parts of a clock.

5) Do not use commas:

in defining/restrictive relative clauses ( 4.2.4), e.g.

This is the first book, that/which he wrote.

to introduce that-clauses (, e.g.

It is thought, that these climatic events will continue.

directly in between a subject and verb, no matter how long the subject ( Appendix 2), e.g.

The most significant discoveries made in this period, were in the field of space exploration.

Colons and Semi-colons

1) Use a colon to introduce a sentence that expands in some way on the previous one, by, for example, providing an explanation, or listing items (see 7 above), e.g.

The graph of points for pairs of snapping shrimps always shows a correlation of the sizes of mates: bigger males pair with bigger females, smaller males with smaller females.

9.1 for information on using colons in referencing

9.2 for information on using colons in quotations

2) A semi-colon can be used instead of a full stop to separate sentences which are closely connected (see 8 above), e.g.

A newborn infant is not a blank page; however, his genes do not seal his fate.

Atoms are assembled into complex molecules; these react, via complex pathways in every cell, and indirectly lead to the entire interconnected structure that makes up a tree, an insect or a human.

5.3 for information on commas, colons and semi-colons in lists

9.1 Appendix 3 for information on apostrophes, hyphens etc.


Add commas, colons or semi-colons to the following sentences where necessary or so that they are easier to follow. Note that some sentences do not require any further punctuation, i.e. it would make them grammatically incorrect.

1) Over the past two centuries pollution has become one of the most pervasive and multi-faceted threats to human health.

2) In 1988 the Centers for Disease Control (CDC) concerned about the spread of HIV in hospitals published a set of universal procedures requiring all medical facilities in the United States to conform to specific guidelines for patient care (Table 6.2).

3) Darwin was concerned with evolution i.e. change over time and he proposed a process natural selection that could bring about such change.

4) Chemical reactions normally occur in water and water can also participate in reactions.

5) If every individual in the world were to demand as much energy as the average person uses in North America the global energy supply industries would require a five-fold increase in their use of primary energy sources.

6) After felling a tree has to be processed in order to render the timber suitable for man’s use.

7) The calculus of variations which plays an important role in both pure and applied mathematics dates from the time of Newton.

8) The computers which form the basis of those used today were mainly developed in the 1940s.

9) Scientists are able to identify parts of the brain that are specifically targeted by addictive drugs.

10) Einstein in his general theory of relativity (1915) proposed that the universe exists in four-dimensional space-time.

11) Aromatherapy users showed prominent characteristics they were far more likely to be younger females highly educated who tend to live in urban areas.

12) The pH of the heartwood varies in different species of timber but is generally about 4.5 to 5.5 however in some timbers such as eucalypt oak and western red cedar the pH of the heartwood can be as low as 3.0.