The Use of the Apostrophe in the English Language
fourmilab.ch
fourmilab.ch
1990s vs. 1990's vs 90s vs 90's vs '90s vs '90's
or the could've, could have, could of corrupted homophone disaster.
Like most things in English, apostrophes kind of have a standard, basic, rule concept (used before an s when making a possessive), then the rest is common exceptions (contractions, plural form possessives) and options (decade ranges) which are only options to certain people and necessary to others, except for the very specific exceptions (plural single letters, quoted plurals, quoted possessives, possessive and plural, words naturally ending in s, glottal stops, un-lettered syllable accents, clicks, silent but looks cool), which nobody remembers correctly except those being pedantic and never seem to really muss up anybody's understanding of the meaning.
Anybody who thinks they know all the apostrophe rules most likely doesn't. Even http://theoatmeal.com/comics/apostrophe which captures some of the complexity mises a bunch of these cases and inserts one I've never seen -- the quoted single letter plural.
The only rule you have to remember is this, "what are the grammar rules that your readers will be assuming are the rules, follow those for comprehension."
Ironically, it is considered a bastion of knowledge by many today. Most of that is due to the depths to which the net has sunk in general. That said, it is a source of real knowledge and insight. When something egregious enough is posted, a real expert is often driven to post an informative reply from their personal experience.
http://theoatmeal.com/comics/apostrophe
But is it just me or the possession example doesn't match with the recap?
"your" ("its") is the possessive.
The contraction <=> apostrophe rule doesn't break for me in this case. How could it break for anyone?
Did you actually mean a noun phrase? :-)
"It's" only "it is".
Even though, it ignores "it has", and would more precisely be:
"It's" is only "it is".
The rule that possessive pronouns never have apostrophes is handy, too.
One rule he alluded to but didn't make explicit is over the possessive form of words already ending in "s". We know that one does not add an "s" if the word is a plural form that already ends with that letter.
What he doesn't directly address is singular words that end in "s". For example, my first name is "Chris". I've seen many people refer to "Chris' stuff", but I believe this is incorrect. Because my terminal "s" was not the result of pluralization, I'm still entitled to a possessive "s": "Chris's stuff".
Because "it" is the only personal that has a possessive form consisting of the personal pronoun followed by an "s".
The briefcase belonging to him is his briefcase, not hims briefcase.
The purse belonging to her is her purse, not hers purse.
The mama belonging to you is your mama, not yous mama.
The nasty case of chlamydia belonging to me is my nasty case of chlamydia, not mes nasty case of chlamydia.
Similarly it's "our" not "uss" and "their" not "thems". I think that's covered all of 'em. So "its" is unique as being the only one where you could reasonably make this mistake.
Some teachers go the extra mile by saying that this rule also goes if the word ends with any consonant pronounced with an S sound; "Alix' room"; but not if it ends with a pronounced S sound followed by a silent vowel; "Belize's beaches". I personally follow this rule.
What would that be, anyway? "Chris's' stuffs"? [edit] n/m, I see this was addressed below.