I've just seen the sentence below in my grammar book:
You still have a lot of paint, so why not paint the bedroom too?
and I thought it should have been:
"You still have a lot of paint, so why don't you paint the bedroom too?"
Am I wrong?
We use 'why not' followed by the base (infinitive) form of a verb (without 'to') to make a suggestion: [You have paint left] why not paint the bedroom? [your car is being repaired] why not borrow Jim's car? [You are bored] why not read a book?
We use 'why' followed by the base form of a verb to suggest that an action is unnecessary or pointless: Why walk when you can ride in a bus? Why eat hamburger when you can have steak? Why complain when nothing will be done?
Both sentences are fine and mean the same thing. Example:
Why not go see a movie tonight?
Why don't we go see a movie tonight?
Note with "why not" you don't have to specify the subject. I might suggest, "Why not paint the bedroom?" because I don't want to help you, but I want to avoid explicitly saying that you will be the one doing the work.
A: Since you're already cleaning the kitchen, why not make dinner?
B: You mean, we will make dinner together?
A: No, I mean you should make us dinner. I'm going to take a nap. Wake me when it's ready?