Dad’s car is orange, but Mum’s yellow car is better.
If the noun in question ends with an S (yachts, readers, gods) an apostrophe is added without the S.
All the yachts’ hulls were damaged in the storm.
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The gods’ decisions are said to be just.
However, many print publications like newspapers and magazines use ’s when a proper noun ends in an S. This is for clarification and a question of style: what you do is up to you.
Athens’s Olympic preparations
Britney Spears’s sordid history
The possessive form of it never has an apostrophe (its). It only has an apostrophe when you mean to say it is (it’s).
CD’S or CD’s
DVD’S or DVD’s
Removing the apostrophe makes the word look more attractive, and we can do it by keeping the abbreviation capitalised and making the S lowercase:
Non-capitalised abbreviations (like laser) do not have apostrophes (lasers).
#'s becomes “hashes”
@'s becomes “at-signs’”
Even spelling out the sound a letter makes can assuage much head-scratching:
S’s becomes “Esses”
I’s becomes “Eyes”
Admittedly, sounds only makes sense in a sentence that has other spelled-out sounds:
There can be no eyes in the document.
There can be no esses, eyes, elles or dees in the document.
Spelling out sounds is a matter of informal style. It is rarely done in professional writing.
When referring to dates in word form, as in the nickname of an era or the general age of a person, the plural form of the word is used:
The roaring sixties
In his early thirties
Using the singular form with an apostrophe creates problems:
The roaring sixty’s
This implies that the number 60 both roars and possesses items.
“Did not” becomes “Didn’t”
“Does not” becomes “Doesn’t”
Sometimes though the influence of popular language an apostrophe becomes left out, as in the much maligned little:
“Little” should become “li’l’”, but thanks to popular usage it is now “li’l”.
No ands, ifs or buts. (there should be no conditions)
No and’s, if’s or but’s. (those words should not appear)
When referring to the word itself, use apostrophes. If referring to the meaning of the word, use no apostrophes.