Apostrophe vs. Single Quote

Solution 1:

An easy way to differentiate:

An apostrophe is only used within or at the very end of a word - it is part of the word.

In English, it serves three purposes:

• The marking of the omission of one or more letters (as in the contraction of do not to don't).
  
• The marking of possessive case (as in the cat's whiskers).
  
• The marking as plural of written items that are not words established in English orthography (as in P's and Q's, the late 1950's). (This is considered incorrect by some; see Use in forming certain plurals. The use of the apostrophe to form plurals of proper words, as in apple's, banana's, etc., is universally considered incorrect.)

Single quotes are only used around words - they come in pairs, and are not part of any word.

Single or double quotation marks denote either speech or a quotation.