adjectives and participles

[Englishfinger]

Hi, I would like to ask why if I want to say that a person has sat (on a chair), I have to say: She´s a sitting person, or a seat person, as I´ve seen in the dictionaries.On the other hand, if I want to say that someone bought a book, I say the book has been bought
I mean, bought and sitting are both adjectives in the 2nd examples. The question is Why do some adjectives come from the participles of the verbs and others do not? Is there any rule that I´ve skipped? If so, how could I find it on the Internet? You know, a particular name, grammar point or that sort of thing.
I´m learning, so, please, correct all my mistakes
Best wishes. Thanks.

[Beeesneees]

hi Englishfinger,

Look at these:

She is sitting down.
She is buying a book.

She sat down this afternoon.
I bought a book this afternoon.

You are confusing the tenses when you compare those two verbs.
'A seat person' is also incorrect. I think you mean 'a seated person'.
_________________
Cheers m' dears!

[Mordant]

There is no rule for which adjectives derive from participles.

It seems that participles are likely to be officially classified as adjectives where no proper adjective already exists. Look at "annoying" and "irritating." But we have avoided "irking," probably because we already have "irksome." Also consider "embarrassed." This is not iron-clad, however. Both "sophisticate" and "sophisticated" are adjectives, the latter far more common and the former nearly always a noun. Frequency determines whether they eventually enter dictionaries as adjectives.

Most adjectives do not derive from participles. And that is a good thing. Our descriptive ability would be limited to existing verbs. I would look at the participial adjectives as a category of adjectives rather than as the standard that has been tossed aside to form adjectives that are not participles.

[Englishfinger]

Yes, you are right! What a silly question I made! Sorry. Thanks