Questions: short forms

In informal situations, especially in speaking, we can reduce questions rather than using complete clauses. Short questions can be clauses, phrases or even single words:

Full form	Short form
Are you hungry?	You hungry? or Hungry?
Is this your pen?	This your pen?

When we shorten questions, the auxiliary verb and the subject are both often omitted (ellipsis):

A:
Got the key? (full form: Have you got the key?)

B:
Yeah.

A:
Working tonight? (full form: Are you working tonight?)

B:
No, thankfully.

Warning:

We cannot omit the auxiliary verb or the subject if the subject is I:

Have I met you before?

Not: Met you before?

Am I really the one for this job?

Not: I really the one for this job?

When we know a lot about the context, we often shorten questions:

A:
Are you looking forward to the party? (full form)

B:
Not really.

A:
Why aren’t you? (full form: Why aren’t you looking forward to the party?)

B:
I’m not a great fan of parties.

When we know a lot about the context, it would be unusual and often too formal to use the full form of the question.

Compare

A: Want to go for lunch now? B: Yeah, great. A: The Diner? B: That’s perfect.	A and B know each other well and they often go to lunch at The Diner.
A: Do you want to go for lunch now? B: Yeah, great. A: Do you want to go to The Diner? B: That’s perfect.	The full forms of the questions are correct but the full form of the second question sounds more formal than the short form.