Apostrophe?

[chillipepper]

A room where teachers relax = teachers lounge A groupof teachers lying around = teachers lounge Where does an apostrophe go?

Also does anyone have a good way, to use as a mnemonic, of rules regarding the apostrophe?

[another-view]

teachers' lounge for the first one. No apostrophe for the second one.

You only put an apostrophe in if there is something that belongs to someone. For example the lounge in the first one is a room belonging to the teachers. As teachers is plural, you put an apostrophe after the S.

The 2nd example describes something the teachers are doing rather than anything belonging to them and so no apostrophe is needed.

[Quizmonster]

Apostrophes are used to show that letters are missing or to indicate possession. �Can't' is short for �cannot', so the apostrophe stands for the missing letters �n' and �o'.
In this phrase...'the dog's tail'...the apostrophe shows that the tail belongs to one dog as it is between the 'g' and the 's'. The same idea applies here...'the dogs' tails'...only this time, there are two or more dogs involved. In such cases, the apostrophe comes after the �s' of �dogs'.
When you have an irregular noun - that is, one that doesn't make its plural by adding �s', such as man/men or child/children - the apostrophe is put at the end of the basic plural word and not after the possessive �s'. For example, you should write...'the men's cars' or �the children's school'.
Always avoid what is known as the greengrocer's apostrophe, which is wrongly used to create plurals as in "Apple's �1.00 for a pound!" instead of "Apples �1.00 for a pound!" Not only greengrocers do this, of course, but they do seem to be particularly prone to it.
Not exactly a mnemonic, I agree, but it does explain how the apostrophe works.

[nescio]

Just to add to QM's answer,
there is always (at least) one anomalous case to b*gger up the system.
It's is a contraction of 'it is', NOT the possessive form of 'it'.
That is written as 'its', WITHOUT an apostrophe.

No confusion there, then.

[Quizmonster]

And there's another one, Nescio, which I deliberately avoided mentioning to avoid confusion. I refer to the situation such as we find in the proverb, "Mind your p's and q's!"
That is invariably presented just as I've presented it and means several of the letter 'p' and several of the letter 'q'...ie both plurals! So, the plural of single letters is formed by adding apostrophe 's'.

How many i's are there in Mississippi?

[chillipepper]

Thanks to all. Not confusing at all!!!!

[Pamelakaren]

Apstrophes are used to show a word has been shortened, as in "isn't" for "is not", however, the use showing possession is the one that most confuses. It's easy! For more than one the apostrophe goes at the end. That is, if there are several teachers and you want to say that the lounge belongs to all the teachers put the apostrophe at the end (teachers') but if the lounge only belongs to one teacher then it goes before the s - (teacher's)