Quotation marks can be single (‘x’) or double (‘’x‘’).
Quotation marks are used in the following cases:
to mark the beginning and end of direct speech (i.e., a speaker’s words written down exactly as they were spoken). In American English, the rule is to use double quotation marks:
"That," he said, "is nonsense."
"What time will he arrive?" she asked.
In British English, quotation marks are called inverted commas, and the single ones are used more frequently than the double for direct speech.
See more information about how to use punctuation in direct speech.
to mark off a word or phrase that’s being discussed, or that’s being directly quoted from somewhere else. In this case, in American English, single or double quotation marks are acceptable but it's important to stick to one way or the other throughout a piece of writing. Any punctuation associated with the word or phrase in question should come before the closing quotation mark or marks:
What does ‘integrated circuit’ mean?
He called this phenomenon ‘the memory of water.’ Next, a hollow spout, known as a "feeder tube," is placed in the hole.
In British English, the usual style is to use single quotation marks, while any associated punctuation is placed outside the closing quotation mark:
Their new single is called 'Curtain Falls'.
Direct speech within direct speech
As we saw above, the rule in American English is to use double quotation marks for direct speech. The exception is when a piece of direct speech is quoted within another piece of direct speech, in which case the internal quote should use single quotation marks. For example:
Professor Flynn began with, "Even if you've never read a word of Shakespeare, I'm sure you've heard 'To be or not to be' a thousand times."
As odd as it may look to American readers, it is perfectly correct in British writing to use single quotation marks for direct speech and double quotation marks to enclose quoted material within. For example:
She still sounds amazed when she says: ‘We were turned down because “we represented too small a minority of the population”. They could still get away with saying things like that then.’