prototypical noun versus element noun

Solution 1:

The article tests three common explanations for use of the definite article in (American) English — familiarity, uniqueness, relevance — and find them wanting, especially in expressions in “prototypical” contexts.

I say American English because one of the most salient differences to British English is that Britons go to hospital and are in hospital for treatment, while Americans do so with the definite article, even when the hospital is not necessarily uniquely identifiable. If Britons go to a hospital for any other reason, say, to visit a patient, then the article is used. This suggests the obvious: what’s topical is that the person is ill or injured enough to require inpatient care, not where they are being treated.

Having a picnic in the park is similar: the picnic is topical, not which park. It's as generic as in the idiom “It’ [not] a walk in the park.”

The authors also mention means of transport — take the stairs, the bus, the train — all along fixed routes. I would argue that the most convenient route to a specific destination qualifies as unique.

I would also argue that if A asks B to open the window, rather than a window, A means the window closest to B, even when there are several windows, since how much air are you going to get from a window several feet away?