#1. Avoid using an apostrophe to indicate a plural. The incorrect use of an apostrophe to form the plural is called the greengrocer's apostrophe, since grocers are often the worst (or at least the most visible) offenders. If you have more than one apple, then write apples, not apple's. If you cannot replace the word with "his," "her," or "their" and if it isn't a contraction, then an apostrophe should not be used.
* People often forget the rules when a word ends in a vowel, such as the word "mango." Many people write "mango's" instead of "mangos" or "mangoes".
* An exception to this use is in the case of making a single letter plural. Therefore, Why are there so many i's in the word "indivisibility"? is correct. This is simply for clarity reasons, so the reader does not mistake it for the word "is." However, in modern usage, the preference is to avoid inserting an apostrophe and instead surround the single letter in quotation marks before pluralizing it: Why are there so many "i"s in the word "indivisibility"?
* Similarly, apostrophes can be used when talking about a word (e.g., this list contains a lot of do's and don't's) but quotation marks can make it clearer ("do"s and "don't"s).
* An exception can also be made for numbers and abbreviations, although some consider this old fashioned, illogical and unnecessary.
o "I bought many CD's in the 1990's." Incorrect.
o "I bought many CDs in the 1990s." Correct.
