LIKE ITALICS and (Chapter 17) hyphens, quotation marks are to be used as sparingly as possible. They should light the way, not darken it.
In handwriting and typing, they are usually indicated thus: “……” or '……', although many people take time to ma their 'quotes' resemble those of printing: “……” or '……'
Formerly “double quotes” were obligatory. Nowadays 'single quotes' are fast becoming very common. An inner quotation differs from the main quotation, in that primary '……' takes secondary “……” and primary “……” takes secondary '……'. 'The more logical course would seem to be that single marks should represent the first quotation and double the one contained in it. Consistency would then require that single marks only should be used in ordinary quotation, ' as T.F. and M.F.A. Husband say in their very good, long-forgotten little book, Punctuation: Its Principles and Practice, 1905. * (See also § 8.)
Quotation marks-too sweepingly stated, by a notable authority in 1893, to be 'now called inverted commas', an inaccurate term and an unrevelatory-are primarily used to indicate the exact words of a speaker or of a text. Obviously 'He said that “he was not a fool”' is incorrect if the second 'he' refers to the speaker. Unless the speaker were referring to a person other than himself, the speaker's words were 'I am not a fool'.
Examples of correct usage (but not of the most complicated usage-see Chapter 22) are these:
You have declared, 'I am Tecumseh Siwash'. But can you prove that you are?
* In a footnote they remark, 'The Clarendon Press follows this method'. So do most writers-at least, most of those writers who can get their own way.