A noun adjunct / the possessive case

Question

Sometimes it’s possible to use either a noun adjunct or the possessive case.

the shop door
the shop’s door

However, in certain phrases it’s not OK to do so.

the ship’s crew (the ship crew is wrong)

The questions are:

1. How can one find out what to use in such cases as “the shop(’s) door” when a noun adjunct option and the possessive case option are available?
2. How can one know which option is wrong in order to avoid the construction “ship crew”?
3. Is there a difference in meaning between (a) the shop door (b) the shop’s door?

Answer 1

These are nice and subtle questions.

Beginning with (3), there is a semantic difference between shop door and shop’s door. If I tell you I’ll wait by the shop door, then I generally mean at the front of the store (or maybe by the door for deliveries), but not, for instance, at a door that separates the shop from the living quarters. The same goes for shop window (usually, not just any window in the shop, but the display window at the front) and shop floor (usually, not the floor out the back where goods are stored, but the parts accessible to the public). By contrast, shop’s door/window/floor can refer to more widely. For instance, Today, I’m going to fix the shop’s floor might well refer to parts out back; and in a related vein, the shop’s side-window is fine, the shop side-window is odd.

Hence, in answer to (1), you use the possessive for a more generic meaning, and the compound to pick out some more idiomatic, conventionally salient door of the shop, etc.

With regard to (2), I’m not sure that ship crew is, in fact, unacceptable. If, in a hotel, we’re trying to stop sailors and pilots from fraternising, I might tell you: Put ship crews on the even floors and plane crews on the odd floors. If there’s a fight, I might ask: Was a ship crew that started it? When ship crew becomes odd is when we have a specific, known ship in mind—in the same way that it’s odd to say the dog owner, rather than the dog’s owner, when the dog in question is known and salient.

Answer 2

The situation couldn't be simpler.

"shop door" is a: type of door.

That would be because, you know, shop is an adjective? :)

Shop door, cheap door, expensive door, pink door, last door, aircraft door, submarine door, waterproof door ... shop door.

Adjective-noun. Couldn't be simpler.

Whereas,

the shop ’s door is: the door of the shop you are referring to.

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shop door, pink door, cheap door: type of door

Adjective.

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John's door, the shop's door, the barn's door: doors belonging to John and others

Possessive "S".

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Again, couldn't be simpler.

Consider say "castle gate". That's the highly decorated, large, baroque, type of gate. (Note, type of gate.)

It would be completely normal to say:

"This castle's castle gate has gold accents, but this castle's castle gate is rusty."

You could also say:

"Here's the castle's castle gate - and over there is the castle's small gate, and over there is the castle's emergency gate."

One point of confusion: "shop door" (i.e. adjective-noun) is an extremely common term. So when you say "The shop's door" it just, happens, to sound similar to that extremely common phrase. No big mystery.

Answer 3

I guess my confusion comes when we use Employee Details and Employee's Details.

I would say: Enter an employee name, but I would say Enter the employee's name. The former being far more abstract, whilst the latter is very specific to the employee I have in mind.

Would it be wrong to say Enter an employee's name?

In my head I see details more like this:

Employee Details - an abstract idea that doesn't specify details about any particular employee. If anything, it highlights/emphasises the details element of the phrase.

Employee's Details - relates specifically to the details of one employee.

Employees' Details - relates specifically to the details of more than one employee. For example, this could be a group/department of employees within a business.

Would this be correct? What are the views?