Way 1 · best default
I'm afraid I can't
Polite and clear. "I'm afraid" here just means "sorry", not that you're scared.
Examples
I'm afraid I can't help this weekend. I'm away.
Sorry, I'm afraid I can't make it on Thursday.
In a conversation
A: Could you water my plants while I'm in Spain for a month?
B: I'm afraid I can't. I'm travelling a lot myself.
Common mistake
Not: I'm afraid I can't to come.
Say: I'm afraid I can't come.
After "can" or "can't" there's no "to": can't come, can't help, can't make it.
