Page 392 - Practical English Usage 3ed - Michael Swan, Oxford

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noun + 's + noun: children's clothes; a bird's nest
In some classifying expressions we use a structure with possessive's.
This is common when we are talking about things that are used by a person or animal: the first noun refers to the user.
children's clothes a man's sweater
women's magazines a bird's nest
Generally, either both nouns are singular or both are plural.
a child's toy children's clothes
but
a women's magazine
Not all 'used by' expressions have possessive's.
baby clothes a birdcage
British and American usage sometimes differ. Compare:
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noun + 's + noun: cow's milk; a hen's egg
The's structure is often used for products from living animals.
cow's milk lamb's wool
sheep's wool a bird's egg a hen's egg (B U T camel hair, horsehair)
When the animal is killed to provide something. we usually use noun + noun.
calfskin chamois leather fox fur chicken soup a lamb chop tortoise shell
parts: a man's leg; a table leg
We use the's structure to talk about parts of people's and animals' bodies.
a man's leg an elephant's trunk a sheep's heart
But to talk about parts of non-living things, we usually use the noun + noun structure.
a table leg (NOT ti table's leg)
a car door (NOT USUALLY a car's door)
pronunciation
Classifying expressions with possessive's most often have the main stress on the first noun. Compare:
- a 'doll's house (a kind of house)
my brother's 'house (not a kind of house)
- 'goat's milk (a kind of milk)
the goat's 'tail (not a kind of tail) Here, too, there are exceptions.
a child's 'bicycle (a kind of bicycle)
For the use of structures with '$ to talk about possession. relationships etc, see 440.
noun + noun, noun + 's + noun, or preposition structure? This is a very complicated area of English grammar. The 'rules' given above
show the general patterns, but unfortunately there is no easy way to be quite
a baby's bottle (BrE) a baby's pram (BrE) a doll's house (BrE)
a baby bottle (ArnE)
a baby ca"iage (AmE) a doll house (AmE)
noun + noun (2): advanced points 386
page 360