but/and

[navi tasan]

Which is correct:
1-Why did you send him a letter but didn't thank him in it?
2-Why did you send him a letter but not thank him in it?

3-Why did you leave us and didn't get in touch to tell us where you were?
4-Why did you leave us and not get in touch to tell us where you were?

 

[MikeNewYork]

Which is correct:
1-Why did you send him a letter but didn't thank him in it?
2-Why did you send him a letter but not thank him in it?

3-Why did you leave us and didn't get in touch to tell us where you were?
4-Why did you leave us and not get in touch to tell us where you were?

Use #2 and #4. They use "why did you" for both parts of the construction.

#1 and #3 try to use "why" and "you" in both parts but not "did". That doesn't work.

 

[blacknomi]

Thank you, I learned something today.

 

[navi tasan]

That's good. So did I. And thank you Mike.

 

[Francois]

Do you often use that construct?

FRC

 

[Casiopea]

Which is correct:
1-Why did you send him a letter but didn't thank him in it?

I agree with Mike's response.

A but not B
2-Why did you send him a letter but not thank him in it?

A and not B
4-Why did you leave us and not get in touch to tell us where you were?

'but not' and 'and not' connect two verb phrases. The auxiliary 'did' is added for the sake of question formation; it's not really part of the verb phrase so you don't have to duplicate it,

Why did you leave us and did not get in touch.... (Not OK)

Why did you send him a letter but did not thank him.... (Not OK)

All the best,