Do 'single quotes' indicate a concept?

Question

1. "Apple" it indicates a word.
2. Apple it indicates a referent (=fruit).
3. 'Apple' it indicates a concept of an apple.

Is it true? I saw on Wikipedia:

Use–mention distinction

Either quotation marks or italic type can emphasise that an instance of a word refers to the word itself rather than its associated concept.

• Cheese is derived from milk. (concept)
• "Cheese" is derived from a word in Old English. (word)
• Cheese has calcium, protein, and phosphorus. (concept)
• Cheese has three Es. (word)

A three-way distinction is occasionally made between normal use of a word (no quotation marks), referring to the concept behind the word (single quotation marks), and the word itself (double quotation marks):

When discussing 'use', use "use".

The logic for this derives from the need to distinguish use forms, coupled with the mandate to retain consistent notation for like use forms.[17] The switching between double and single quotes in nested citation quotes reveals the same literary device for reducing ambiguity.

Answer 1

I tracked down reference 17 from the Wikipedia quote (Butcher's Copy-editing):

Some authors have their own system of quotation marks, which they are anxious to retain: for example, double quotes for speech and single for thoughts, or double quotes for quotations and single quotes for words or phrases used in a special sense. Try to persuade your author not to do this, as it can be more confusing than helpful. If you do retain an unusual system, warn the typesetter not to ‘correct’ it.

In other words, while Butcher did see an author use this quote style, it is very much not the norm and her recommendation is to not do that! (I've never seen this distinction made myself.)

Answer 2

There is no widely agreed convention. If you as an author wish to use some convention like the one you cite, you can feel free to do so. But if you didn’t explicitly describe (in some metadiscourse) the convention you were going to be using, your readers would be unlikely to catch it on their own. And they’d probably resent you for the trouble you had put them to to work out such a subtlety.

Answer 3

I think I can safely say that these days, the type of quote used has more to do with context than syntax/logic.

So, for example, if I wanted to talk about it here, I might refer to "An Apple" and use double-quotes as a form of highlighting / delineation.

But in another example, I might wish to refer to another author saying exactly the same thing. So in that case I would put the quotation in double quotes, and shift the inner phrase to singles, to emphasise that it isn't the end of the outer quote:

A.N. Other: "I have scientific proof that 'An Apple' exists."

Answer 4

I admit, I’ve sometimes caught myself using single quotes this way, so I must have seen it somewhere, but no style guide recommends it and it’s not standard.

In American English, the usual convention is that the first level of quotation marks (outer quotes) are always double quotes, and all quotes within quotation marks (inner quotes) are single quotes. (It is extremely rare to have quotes within quotes within quotes, but if you do, make it a block quote.)

In some older forms of British English, it used to be the other way around: outer quotes were single and inner quotes were double. Today, though, the only significant difference between British and American quotation style is that punctuation added to a quote to make it fit into the rest of the paragraph goes inside the quotation marks in American English, but outside them in British English.