meaning - Is the past tense correct in "Did you know Fred was a doctor?"

Possible Duplicates:
He didn't know where New Jersey was…
Tense change: previous actions on something that's currently true

My wife and I were disagreeing about this today:

1. Did you know Fred was a doctor?


2. Did you know Fred is a doctor?

I was arguing for (1) based on what seemed to "sound right." My wife claimed that, since Fred is currently alive and still practicing medicine, present tense should be used. However, we agreed that the negation of these sentences uses was:

I didn't know Fred was a doctor.

Here I think everyone would agree that is would sound wrong!

So which is correct between (1) and (2)? And why? Is this some kind of subjunctive?

Answer

My vote for "is" in both cases, negated or not. If you have the qualification, then you are a doctor.

Compare

Did you know that Fred is a doctor? - Oh, is he? I'd never have guessed.

with

Did you know that Bob was a fighter pilot in the war? - Oh, was he? I'd never have guessed.