Punctuation is an important aspect of any written text. Good punctuation organises or divides the text to make meaning clearer; poor punctuation will make it difficult to understand.

2.1 General guidelines

Use common sense. Punctuation should help make written language clear to readers. If it does not, it should not be there.

2.1.1 Precedence

With the exception of quotation marks, brackets and ellipsis points, never use two or more punctuation marks together. Always use the stronger or more necessary one. For example, question and exclamation marks are stronger than commas and full stops. In the first of the two examples the question mark fills the role of the comma; and in the second, a full stop is not used after the exclamation mark.

2.1.2 Punctuation and spacing

Punctuation marks in English – apart from dashes, ellipsis points and slashes – are always closed up to the preceding word.

Slashes are closed up to the preceding word and to the next word when they separate two single words.

When a slash separates two groups of words or a group of words from a single word, insert a space before and after the slash.

Full stops, question marks, exclamation marks, commas, colons and semicolons are always followed by a single (not a double) space.

2.2 Full stops

Full stops or points present few problems. Use them for three main purposes: ending sentences that are not questions or exclamations, punctuating the numbers or letters used to list the elements of a summary, and separating the letters in some, but not all, abbreviations.

2.2.1 Indirect questions

Use a full stop, not a question mark, after an indirect question.

2.2.2 Elements in lists

Use full stops after the numbers or letters used to list the elements of a summary.

The individual items in vertical lists should only be followed by full stops when they form complete sentences (as above), not when they are simply nouns or noun phrases (as below).

Punctuate information contained in a list written in sentence form with a comma after each item in the list and a full stop after the last one.

If the list includes sentences or phrases punctuated with a full stop, the clause introducing the list must end in a colon (as in the example) or a full stop.

2.2.3 Headings

Do not use full stops in most headings.

However, use full stops (not colons) in run-in heads, which should be italicised or written in boldface to make them stand out.

2.2.4 Sentences ending in abbreviations that take a final point

In declarative sentences, if an abbreviation that takes a final point ends the sentence, finish the sentence with just one final point / full stop.

In the case of questions and exclamations, however, finish the sentence with the final point of the abbreviation followed by a question mark or exclamation mark.

2.2.5 Footnotes and endnotes

Whether or not they form complete sentences, end all footnotes and endnotes with a full stop.

2.3 Colons

Use colons mainly to introduce quoted passages of text, explanations, examples or summations and long or complex lists. A colon is nearly always preceded by a complete sentence; what follows it may or may not be a complete sentence, and may be a list or even a single word.

2.3.1 Common mistakes with colons

Colons are frequently misused in the following situations.

i) Comma substitution

Do not use a colon to substitute a comma. Therefore, not

but

ii) With for example or such as

Do not use colons with for example or such as, which serve the same purpose as a colon. Therefore, not

but

iii) After a preposition

Do not use colons between a preposition and its complement. Therefore, not

but

iv) Two or more colons in a sentence

Never use more than one colon in a sentence.

Note, however, that you can use a semi-colon and a colon together in the same sentence.

2.3.2 Other uses of colons

i) Separating a title from a subtitle

When citing the name of a book which has both a title and a subtitle, separate the two with a colon. Do this even though no colon may appear on the cover or the title page of the book itself.

ii) Writing ratios

Use colons to write ratios.

However, in more formal contexts write out ratios in words.

2.4 Semicolons

2.4.1 Main functions of semicolons

The semicolon is mainly used to join two complete sentences in a single sentence when (a) the two sentences are thought to be too closely related to be separated by a full stop and (b) there is no connecting word which would require a comma, such as and or but.

2.4.2 Alternatives to the semicolon

i) Full stop

A semicolon can generally be replaced by a full stop.

However, the semicolon suggests that the two smaller sentences are more closely related than the average two consecutive sentences.

ii) A connecting word

A semicolon can also be replaced by a suitable connecting word (and, or, but, while, yet) with a joining comma.

However, certain connecting words must be preceded by a semicolon or full stop. The most common among these are consequently, hence, however, meanwhile, nevertheless, therefore and thus.

2.4.3 Using semicolons

A semicolon must be preceded by a complete sentence and followed by a complete sentence, unless it is used as in one of the two exceptional cases explained in Section 2.4.4 Using semicolons in exceptional cases.

2.4.4 Using semicolons in exceptional circumstances

Semicolons may be used to separate sequences of a sentence in two special circumstances.

i) Long sentences with many commas

If a sentence is so long and so full of commas that it cannot be easily understood, use a semicolon to mark the most important break in the sentence.

However, it is often better to split a very long sentence into two separate sentences.

ii) Long or grammatically complex lists

Use semicolons to separate long or grammatically complex items in a list, or to make them more conspicuous than they are with commas. For example, use commas with a list of persons, places or dates, but use semicolons when the items are reasons, examples or findings.

When items in a series involve internal punctuation, separate them by semicolons for the sake of clarity.

2.5 Commas

As a general rule, commas can be used to list items in a series, to join sentences and to set off parenthetic or introductory phrases (for commas in lists in sentence form, see Section 2.2.2 Elements in lists).

2.5.1 Listing items in a series

In a list containing a series of items, separate the items with serial commas. However, a serial comma should not precede the conjunction before the final item (in other words, write a, b and c and not a, b, and c). But if a comma would make the meaning clearer, use it – especially where one of the items in the list is already joined by and.

2.5.2 Joining sentences

When you join two complete sentences into a single sentence, you can use commas but follow them with a suitable connecting word: and, or, but, while or yet.

The comma is not required if the subject of the second part of the sentence is omitted or if the conjunction used is and or or.

2.5.3 Setting off phrases

If a phrase is meant to complement or introduce the main information in a sentence, it can be set off by a comma or pair of commas.

i) Defining relative clauses

In relative clauses do not use commas if the clause defines the antecedent and if omitting it would radically change the meaning of the sentence.

The above clauses define the type of students referred to.

In defining clauses that do not refer to people use either which or that.

The above clauses define the type of materials referred to.

ii) Non-defining relative clauses

Sentences with non-defining relative clauses need commas because the clause adds information to an otherwise complete sentence.

In non-defining clauses, only use which or who.

In the following two sentences, which are both correct, the comma makes a difference. In the first, Dr Smith researches only those additives that pose a risk; in the second, the implication is that all food additives pose a risk.

2.5.4 Other uses of commas

Separate a city from a state, province, region or country with a comma.

Do not use a comma between the month and the year.

In most numbers of one thousand or more, use commas between groups of three digits, counting from the right.

Exceptions are degree temperatures, year numbers of four digits, addresses, page numbers and other uses of numbers for a non-quantifying purpose (see Section 5.2.2 Numbers and commas).

2.6 Dashes

A dash is similar in appearance to a hyphen, but is longer and used differently. The most common version of the dash is the en dash. Use it with spaces to make a parenthetical reference.

Use it without spaces to express a connection or to indicate a date, time or number range.

Remember that ranges can be expressed by an en dash or by the words from and to (or between and and), but never by a combination of from (or between) and an en dash.

2.7 Brackets

2.7.1 Round brackets

Round brackets are primarily used in four situations.

i) Secondary or marginal information

Use round brackets to indicate information that is secondary or marginal to the main idea of the sentence.

ii) Explanations or abbreviations of preceding information

Use round brackets to expand on or explain preceding information.

When a passage within round brackets is at the end of a sentence, of which it is only a part, place the full stop after the closing bracket. However, when the bracketed passage is a complete sentence, place the full stop before the opening bracket and then add a second full stop before the closing bracket.

iii) Options

Use round brackets to represent options.

iv) Enumerations in a body of text

Use round brackets to enclose numerals or letters in an enumeration in the body of a text. Use roman type rather than italics for the numerals and letters.

2.7.2 Square brackets

Square brackets are less common than round brackets. They are primarily used in three situations.

i) Clarifications within quoted text

Use square brackets to set off a clarification within quoted text.

ii) Optional or tentative passages

Use square brackets to indicate optional passages or those still open to discussion in administrative texts.

iii) Brackets within brackets

Use square brackets to indicate parenthetical elements that are already in round brackets.

2.8 Question marks

2.8.1 Direct questions

Place a question mark at the end of any sentence that is a direct question.

If the question is a direct quotation, repeating the speaker’s exact words, a question mark is still used.

2.8.2 Other types of questions

i) Indirect questions

Do not use a question mark in an indirect question, in which the speaker’s exact words are not repeated. Use only a full stop, since the whole sentence is now a statement.

ii) Courtesy questions

If a request or instruction is put as a question for reasons of courtesy, do not use a question mark.

2.9 Quotation marks

Use quotation marks, also called inverted commas, to indicate direct quotations and definitions.

Always use double marks for a quotation and single marks for a quotation within a quotation.

Punctuation should be placed according to the meaning: if it belongs to the quotation, it is quoted; otherwise, it is not.

Quotations of over four lines in length should be set off from the text as a block quotation, not enclosed in quotation marks, and single-spaced. Quoted matter within the block quotation is set off with double quotation marks; quotations within these quotations, with single quotation marks, and so on.

Single quotation marks can also help show the reader that a word or term is used in an unusual, colloquial or ironic way.

However, if you overuse quotation marks in these ways, they lose their effect.

2.10 Exclamation marks

An exclamation mark is used at the end of a short phrase or a sentence that expresses very strong feeling. It is one way of adding emphasis and in our institutional context it may be used in public announcements of certain kinds, university relations and advertising.

However, exclamation marks are very rare in formal English, so use them sparingly. Finally, never use two or three exclamations marks in a row.

2.11 Apostrophes

In general, we use apostrophes to indicate possession or contracted forms.

2.11.1 Apostrophes for possessive forms of nouns

The possessive form of a singular noun is marked by an apostrophe followed by s.

This rule applies in most cases even with a name ending in -s.

If a plural noun already ends in -s, the apostrophe is used alone.

Note that the apostrophe is also used in expressions of time periods.

Degree titles should be written with an apostrophe followed by s.

But note the exception: doctoral degree, not doctor’s degree.

Do not use apostrophes to indicate a decade, a plural acronym or the plurals of figures.

2.11.2 Apostrophes for contractions

Use apostrophes for contractions (you’re for you are, don’t for do not, it’s for it is or it has) but note that contractions are far less common in formal texts than they are in informal writing.

2.12 Ellipsis points

Ellipsis points with a space on either side are used to denote missing words from the middle of a direct quotation. Used at the end of a sentence without a space, they indicate that the sentence has been left unfinished.

Do not use ellipsis points to indicate an incomplete list.