English Grammar: Possessive Case

Note that 's means that the next word belongs to the one with the 's.

It is my mom’s bag = the bag belongs to my mom.

It is my friend’s mom’s bag. Who belongs to whom? The bag belongs to my mum. And my mother is my friend's mother, as if she "belongs" to my friend.

And what does this sentence mean: This is Anna's grandfather's book? The book belongs to the grandfather, and the grandfather “belongs” to Anna.

What if a grandfather has two granddaughters, Anna and Jane? They have him in common, here Anna and Jane are one. In this case, we add 's only to the last one in the list of "owners": This is Anne and Jane's grandfather.

And if we have two grandfathers, Anna’s and Jane’s (and they have different names), then we need to add 's after Anna and after Jane: These men are Anne's and Jane's grandfathers.

Let's look at the pronunciation of all these 's. 

The ending of the possessive case is read:

• as [s] after deaf consonant sounds;
• as [z] after voiced consonants and vowels;
• and as [iz] after s, ss: [s]; sh: [ʃ]; ch, tch: [tʃ]; x: [ks].

Examples: 

• cat's [kaets]
• dog's [dɑːɡz] 
• Mary's [‘meri:z’]
• actress's [ˈæk.trəsiz]

'S can be used with animate nouns – animals and people. You can also use 's for collective nouns – groups of people or animals (e.g. family, society, government, company, wolf pack, herd, etc.): This is my family’s house. This house belongs to my family.

You can also use 's with the following inanimate nouns: 

1. with unique objects (the sun's warmth, the wind's strength);
2. with geographical names (New York's parks);
3. with time periods (today's events);
4. with measures – length, time, mass (a day's work, a dollar's worth, five kilometres' distance).

We can also use 's to indicate someone's location:

• I was at my sister’s (house) = I was at my sister’s.
• I need to go to the chemist’s (shop) = I need to go to the chemist’s.
• I bought a newspaper at the newsagent’s (stand) = I bought a newspaper at the newsagent’s.

Hairdresser’s, greengrocer’s, fishmonger’s, jeweler’s – the names of the establishments inherited the names of their owners' professions. 

And for inanimate objects, we use "of the..." rather than 's.

• I saw the top of the page. NOT I saw the page’s top (the top belongs to the page, but we don't use 's because the page is an inanimate object). 
• I felt the softness of his skin. Not his skin’s softness (softness belongs to the skin, but the skin is inanimate, so we do not use 's). 
• I hit my hand on the corner of the table (the table is inanimate, so you cannot write “on the table's corner”). 

When we say that it belongs to "him", "us", etc., we use possessive adjectives and possessive pronouns.