Quotation marks, inverted commas and ‘66 and 99’. Do you know the difference?

In fact, quotation marks, inverted commas and the so-called ’66 and 99’ are the same, but they come in two typologies: double (“...”) and single (‘...’). Either is acceptable, but you must be consistent with your use of them in a piece of writing. In AU texts, however, the following is recommended.

Double quotation marks
Double quotation marks are used to mark the beginning and end of a quote or direct speech. Remember to place commas and full stops inside the quotes, if you are quoting a full sentence:

✔ “I look forward to having physical lectures at the university again,” the professor said.

If you are quoting a fragment of a sentence, place commas and full stops outside the quotes:

✔ The professor was looking forward to “having physical lectures at the university again”.

We do not recommend that you both italicise and use quotation marks in a quote/direct speech at the same time:    

✘ “I look forward to having physical lectures at the university again,” the professor said.

Single quotation marks
Single quotation marks are used to indicate idiomatic/unknown terms or concepts as well as quoted words or sentences within the main quotation:  

✔ He went to the university in ‘the swinging sixties’.

✔ “Let’s explore the meaning of the quote ‘It was the best of times, it was the worst of times’,” the lecturer said.