This depends on where you are publishing your book or story. In the UK, generally, single quote marks are used for dialogue. In the US and some other countries, generally, double quote marks are used for dialogue.
There are different conventions in different parts of the world for how to use quote marks for dialogue.
In the UK, generally, single quote marks are used to indicate that a sentence or passage is speech, as shown in the example below.
‘How much do those bananas cost?’ he said.
In the UK, generally, double quote marks are used to indicate when one character tells of what another character has said, which can be thought of as dialogue within dialogue, as shown in the example below.
‘He just shouted “Go away!” and slammed the door.’ she said.
Hypothetically, you could also have dialogue within dialogue within dialogue, for which you could use triple quote marks, or dialogue within dialogue within dialogue within dialogue, for which you could use quadruple quote marks, but it’s very rarely that anyone needs to do this.
In the US, generally, the rule is the other way round – double quote marks are used to indicate that a sentence or passage is dialogue, and single quote marks are used to indicate dialogue within dialogue. This means that the above two examples would instead be as below.
“How much do those bananas cost?” he said.
“He just shouted ‘Go away!’ and slammed the door.” she said.
All of this is made more complex by the fact that some authors and publishers in the UK use the US convention. In other English-speaking countries, a mixture of the two conventions is used, though more often it tends to be the US convention.
Using single quote marks for thoughts
Some people propose using double quote marks for speech and single quote marks for thoughts.
The disadvantage of doing this is that, because quote marks are such small characters, when you’re reading through a passage of text, it’s easy to miss whether a quote mark was a single quote mark or a double quote mark, and so the reader might think that a sentence that is a character’s thoughts was actually something they said out loud. This means that the reader may have to go back through the text and check which type of quote mark was used, which slows down reading.
The usual way of representing a character’s thoughts is by putting them in italic text.
Advantages and disadvantages of the two conventions
One of the advantages of the US convention is that double quote marks are easy to identify when reading. Single quote marks – particularly the closing single quote mark – look like apostrophes. This can make it harder to see where character speech ends – the reader must use their knowledge of which words are often written with apostrophes in order to determine whether a given mark is an apostrophe or a closing quote mark. With the US convention, this is less of a problem.
One of the disadvantages of the US convention is that it is less conceptually symmetric. For dialogue within dialogue, using the UK convention, you just increase the number of quote marks for each level of dialogue within dialogue, starting with single quote marks, then double, then triple, then quadruple, et cetera. Using the US convention, you can only go two levels in: first using double quote marks, then single. (One way around this is to alternate between double and single quote marks, but this can be difficult to read.)← Writing FAQs