[Grammar] If I knew

[beachboy]

I don't know why he's sad.

1) If I knew why he's sad, I'd try to help.
2) If I knew why he was sad, I'd try to help.


I don't know where he lives.

3) If I knew where he lives, I'd drop by.
4) If I knew where he lived, I'd drop by.

Which of these sentences above are right?

 

[Phaedrus]

I myself prefer (2) and (4), which exhibit backshifting. Compare: I wish I knew why he was sad. / I wish I knew where he lived.