Rev-
There are two different functions of the apostrophe:
- To indicate possession
- To stand in for a missing letter or letters
Let's take these in turn:
1)
to indicate possession -- or, more precisely, to turn a noun into its possessive form. Singular nouns are made possessive by adding a 's:
the boy's hat
the box's contents
the class's teacher
(The last one is somewhat controversial, as some people will say that "the class' teacher" is ok, too. But, as everyone agrees that "the class's teacher" is correct, it may be best to stick to that.)
Plural nouns that end in s are made possessive by adding an '
at the end of the word:
the boys' hats
the boxes' contents
the classes' teachers
Plural nouns that end in a letter other than s are made possessive by adding an 's:
the data's implication
the deer's pelts
the fish's scales
Notice that, when the singular and plural forms of the noun are identical, this leads to ambiguity. Of course the ambiguity is there whether you are using the possesive form or not.
One final important rule:
possessive pronouns do not have apostrophes. Hence:
his is the possessive form of he/him
her is the possessive form of she/her
my is the possessive form of I/me
your is the possessive form of you
its is the possessive form of it
2)
to stand in for a missing letter or letters -- the typical case for this is in a conjunction. Remember, the apostrophe stands in for the missing
letters, not missing spaces. Hence:
isn't for is not (the ' replaces the o)
can't for can not (the ' replaces the no)
let's for let us
we've for we have
you're for you are
that's for that is
it's for it is
zip's for zip is
y'all for you all
And so on. Another use of the apostrophe to stand in for missing letters is in indicating dialect:
walkin' for walking
bloody 'ell for bloody hell
Also note
the '70s for the 1970s (the ' replaces the 19)
class of '03 for class of 2003
3)
what about plurals? -- lots of people think they should use 's to form plurals in certain cases. Lots of people are wrong. This is true even when forming the plural of an acronym, etc. So we have:
Nvidia makes GPUs.
My GPU's a piece of grap. (conjunction for GPU is)
My GPU's performance is terrible (possessive singular)
Nvidia GPUs' performance characteristics are mysterious
There are arguably some exceptions, where the apostrophe serves to seperate the base form of the noun itself from the s that makes it plural. For example:
mind your p's and q's
There are four t's in this sentance.
What is different about these examples is that, without the apostrophe, there would be no way to seperate the base noun (in these cases a single letter) from the s that makes it a plural if one did not insert an apostrophe. This is not true with an acronym like GPU, so there's no need for the apostrophe. Nor does one need to say "I got all A's" when "I got all As" is probably clear; still, the first form is more popular, probably due to the fact that As looks like the word "as".
Regarding your unsuccessful office flirtation, I'd (conjunction for I would) have to say that you unfortunately crashed and burned in grammar as in love. When your sulty coworker wrote "Zips usually all the way up," she was presumably using an incorrect word order variant of "Usually zips all the way up," itself an acceptable colloquial shortcut for "It usually zips all the way up."
Assuming she was using the word "zip" as a verb, there would be absolutely no place for an apostrophe in "zips". My guess is that you thought she meant "zip" as a short form of "zipper", and that her sentence was thus, "(The) zip(per i)s usually all the way up." Dude, I don't know why you would think that--unless you were tripped up by her putting "usually" in the wrong place--but if she actually had intended "zips" to mean "zip (a noun) is", then yes, she would have been missing an apostrophe.
Hmm...actually, taking a glance
at the dictionary, it would appear that "zip" actually is an acceptable short form for "zipper". This is a bit of a surprise to me, as I certainly wouldn't use the two interchangably, but apparently it is correct to do so. I'm still guessing your clothing-challenged colleague meant "zips" to be a verb, not a noun.
Finally, the grammatically correct response to "Can you help me zip it up?" is always "OK." I know Tag is a bit of a grammar nazette, but this applies even in your distasteful public quest to statutorily rape her.
Your wife is very lucky that she married such an idiot.