"Key to" vs. "key for"
Key to exercises.
Today I saw the quoted sentence when looking at the keys to exercises, and afterwards that sentence got me thinking why the preposition to is used here instead of for.
The way I see it is that the key purpose is to match our answer with the correct one; hence, for would fit here nicely. Am I right?
As I stated in comment, keys in the standard sense pair with locks. Copies can be made, but in theory, each lock has only one key that unlocks it. See also:
- keys to the kingdom
- key to my heart
- under lock and key