Riddle me this:
I am an instrument if I am joined with a board,
To which you could use me to play an abundance of chords.
I am a foundation if I am joined with a stone,
To which you and things associated could depend on me alone.
I am a provider of access if I am joined with a card,
To which I can open without disregard.
I rhyme with a word similar to I and myself.
I am often used in a space surrounded by bookshelves.
What do I do for doors, I can do for ideas.
Can you guess what I am, or is the answer unclear?
I made up this riddle for fun. Hope you enjoy!
Hints for the answer are below.
Not only do I open, but I first unlock;
Though if I am not in hand, you might knock knock knock.