1 When you say about a bird in general, you say "This is a feather of a bird", you can also say "This is a bird's feather".
a. So when you say "These are feathers of a bird", so will you say "These are bird's feathers" or "These are a bird's feathers"?
b. You will not say "This is a cage of birds / This is a birds' cage", because there is not a cage belong to all birds in the world, right?
2 When you say about a bird in particular (the bird you bought yesterday), you say "This is the cage of the bird", you can also say "This is the bird's cage".
a. So when you say "These are the cages of the bird" (several cages for one bird), will you say "These are bird's cages"?
b. So when you say "This is the cage of the birds (the birds you bought yesterday / one cage of those birds)", so would you say "This is the birds' cage"?
- When you say about a man in general, you say "This is a wallet of a man" / "This is a man's wallet", you can also say "These are wallets of men. / These are men's wallets.".
But you will not say "This is a wallet of men. / This is a men's wallet." because there is not a wallet belong to all men in the world, right?
- But when you say about a men in particular (the man you told to me yesterday):
a. You can say "These are the wallets of the man." / These are the man's wallets.", right?
b. And if those are some men, you can say "This is a wallet of the men." / "This is a men's wallets.", right?
Thanks!