| In Summary
Full-stops/periods Commas Semi-colons Colons |
In English, punctuation helps make the meaning of a sentence unambiguous. A coherent sentence requires appropriately used punctuation and this will depend on the kind of sentence written and the message meant. The wrong punctuation could change the meaning completely. Compare the following examples:
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In the first sentence, only the grades are frequently changed, which the students do not like, whereas in the second sentence, the fact that grades are changed often upsets the students.
The most commonly confused punctuation symbols are the comma, colon and semi-colon. In the tables below, you will find information about these and examples of their use. It is important to be aware of their functions in the English language as punctuation rules are not always the same in all languages.
Comma
| Use | Example sentences | Remarks |
| 1. Introductory phrases
(to separate “preliminary” words or word-groups from the rest of the sentence, often adverbs) |
At present levels of growth, industry will soon be back on track.
At present, industry needs more investment to get back on track.
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Here the sentence needs the comma to show the reader where the pause comes. Otherwise the reader will not understand the meaning until the end of the sentence is reached. |
| However, common practice is to remove the…
However common it may be to ignore this input, we should nevertheless…
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Again both examples are correct but in the first, “however” has the same meaning as “but” and should be separated with a comma, but in the second the meaning is more “it doesn’t matter how common it may be” and therefore the “however” belongs to the rest of the phrase | |
| 2. Additional information
(to include extra information in a sentence) |
The building, as mentioned previously, will be situated…
The fuel valve, a solenoid gate valve, consists of…
This action is optional (though recommended).
Metal – either steel or aluminium – is used to facilitate the process. |
Sometimes brackets (parentheses) are used if the comment is a stronger, explanatory one. Dashes can also be used for this though they are more informal. |
| 3. Relative clauses
(to enclose a non-defining relative clause i.e. when it provides extra information and is not essential to the sentence. This is a clause which begins with who, whose, whom or which) |
The cable which is next to the machine needs to be plugged in.
The cable, which is next to the machine, needs to be plugged in.
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The first example is defining, it explains which of several cables is being referred to; the second is non-defining (i.e. provides extra information); it simply explains where the cable is. In the second case, there is probably only one cable and thus it is enough to say “the cable” without explaining further.
N.B.: A relative clause beginning with “that” is considered defining (necessary) and is used without commas. The first example here could also read “The cable that is next to the machine needs to be plugged in.” |
| 4. Clarity
(to increase the clarity in possibly ambiguous situations) |
Accept the applicant using procedure A.
Accept the applicant, using procedure A.
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In the first, you are told which applicant to accept whereas in the second, you are told how to accept the applicant. |
| 5. Lists
(to separate items in a list) |
I bought a computer, a disk-drive, a printer and a CD burner.
The different colors were green and blue, blue, black and blue, and white.
The book contained an interesting chapter on molecular structure, a comprehensive list of references, and advice on structure. |
A serial comma can be used to separate the last item in a list, as in the last two sentences. Often, this is done in order to avoid misunderstandings. The comma is then placed before the last separating “and” (see also Semi-colons no.1) |
| 6. Adjective separation
(to separate adjectives in a series unless the adjectives belong together) |
single, variable inputs…..
a mobile, air-operated starter…
but not: bright, red cables |
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| 7. Complex sentences
(to link a dependent and an independent clause when the dependent clause starts the sentence) |
Although it has stopped raining, I don’t want to go outside.
but: I don’t want to go outside although it has stopped raining.
When I leave Chalmers, I want to get a good job. but: I want to get a good job when I leave Chalmers. |
The dependent clause comes first here and thus is followed by a comma. When the dependent clause comes second, as in the second example, no comma is used to separate the two clauses. |
| 8. Numbers | 3,657,435
3 657 435 |
When writing large numbers, commas are used to divide the numbers into groups of three.
However, often no commas are used at all but separated with a space so that the numbers are clearer internationally |
Semicolon
| Use | Examples | Remarks |
| 1. Compound sentences
(to connect two independent phrases in a sentence where the meaning is closely connected and no coordinating conjunction is used) |
Some people work best in the mornings; others do better in the evenings.
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This would work equally well as two sentences but ”flows” better when connected as they are so closely linked in meaning.
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| 2. Longer lists
(to separate long items in a list. Compare with Commas no.4)
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This task involves reading through the text; answering the questions with full, clear sentences; comparing your answers with your partner’s; and finally checking them with the answer key. | It is up to the writer to decide whether commas or semi-colons are needed, though certainly if there are commas within the list e.g. “full, clear sentences” semi-colons are clearer to avoid confusion. |
Colon
| Use | Examples | Remarks |
| 1. Introducing a list | We need three kinds of support: economic, moral and political.
The three kinds of support we need are: economic, moral and political.
This task involves: reading through the text, answering the questions with full sentences, and comparing your sentences with your partner’s etc.
This task involves
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Note here that the information before the colon should be a full sentence when continuing on the same line.
The second sentence is not possible.
Here capital letters are often used if writing full sentences.
It is also possible to mark the points with bullets or numbers to make them clearer. |
| 2. Introducing a subdivision of a subject, e.g. in a title | Typical punctuation problems: the comma
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The phrase after the colon here is a subdivision of the main subject. |