>>>>I didn't know exactly where I would be be right... it's a Heisenbug.
>>>
>>>One philologist was just the other day explaining to me why both are OK but have different meanings - my being the one that still holds, yours being one that held at the time when the sentence happened. But he's in Toronto... any substance in what he says?
>>
>>I had to look up what a philologist is. Maybe both are right for different meanings but I can't see it. "I don't know exactly where I'll be" sounds right.
>>
>>You could think of my version as "I didn't know exactly where I would be be [being]"
>
>OK, found it. Here's what the guy says:
>
>"She said she would come" - means that her arrival may be in the past already; it was in the future at the time. ""She said she will come" - means the arrival has definitely not occurred yet

Hmmm. But her intention at the time was that she would come. It's possible she's changed her mind and/or cannot anymore. Thus her intention at the time is not necessarily the reality of today.

>
>"She said Niagara Falls is an ugly little town" implies a permanent truth, was valid then, is valid now;

But how could she predict that it would permanently remain ugly? She can only give her opinion of that time.

>"She said Niagara Falls was an ugly little town" leaves a possibility that something has changed meanwhile (i.e. nuclear bomb fell on Clifton Hill), so we only know for sure that it was true at the time.

That only works with American bad grammar. If that were the case it should read "She said Niagara Falls had been an ugly little town"