Quote Originally Posted by ShakeyX View Post
With words like больна and закрыт, wouldn't these be considered pure adjectives, as you can use them with no implication of the past (or of any action atall, merely a state in the present)?

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Just putting my thoughts out there as I saw the old сломан and thought to myself, are russians seeing (был) сломан (it was broken) and then inferring it must be broken in the present, or like in english, have the word "broken" got the status of full adjective and has gained meaning beyond its use as a past participle?
You are right. Открытый, закрытый, сломанный should be considered adjectives in most cases, not past perfective participles, since there isn't any 'perfectiveness' in their lexical meaning:
Магазин закрыт на ремонт.
Магазин открыт с 9-ти до 7-ми.
Это закрытая информация.
Я оставил дверь открытой.

On the other hand, they can be used as normal participles too:
дверь, закрытая на замок
игрушка, сломанная ребёнком


Quote Originally Posted by ShakeyX View Post
Likewise I imagine without the status of full adjective you could not use it as a predicate: летящая птица but not птица летящая (unless inverting the words for stylistic reasons). You would surely have to use птица летит.
Птица (есть) летящая makes no sence in Russian, since the Present Active verb is just летит.