When Amelia Pond's parents were erased from history prior to our first seeing her in 11th Hour - why didn't Amelia - and River - cease to exist?

She didn't "forget" her parents and they weren't just killed and disintegrated - they never existed. If they didn't exist, they couldn't have had Amelia - and she couldn't have had Melody - and so on right down her family line.

Bloody hell my head hurts!!

Easy one. Things fell through cracks in time because the Universe was in the early stages of breaking down and when the universe
breaks down we can't expect the laws that govern it to remain intact. In this case the physical laws governing cause and effect
broke down therefore it was temporarily possible to have the effect without the cause ie Amy without parents

Are you saying that was the reason given in ther series or by the writers/producers or is that just your personal theory?

I don't have the whole series and have none of the series 5 DW Confidentials.

My theory based on what was said in the series

Can you clarify - what was said or which episode that was said in?

I think it was established by example that even when the crack erased stuff, the consequences of that stuff still remained.
Notably the duck pond without ducks TEH, the "cracked" clerics protecting Amy being remembered by Amy in FaS etc.

So that explains why Amelia still existed after her parents were gone (but not, why she didn't fall through the crack though it was very close).

It does not explain either why River continued to exist when Rory got killed/"cracked" - even though this was prior to their wedding night => at this time, River was deffo a paradoxon.

Remember when the Doctor reminded Amy she had been living in that big house all alone and she said what about it?
He told her that her parents had fallen through a crack in time, no longer existed, and had never existed and she said she had never had any parents.
This shows that the physical laws governing cause and effect had broken down.
The cause ( Amy's parent's ) had never existed but the effect ( Amy ) was standing right there in front of the Doctor.

Perhaps that's why he kept saying things like "doesn't it bother you that your life doesn't make sense?".... we don't know, she's meant to be stronger and different from a lot of humans somehow... perhaps the whole travelling in the TARDIS thing created a retro-active paradox that kept her in existence.. or something.
Other possible explanations include the writers: "Oops, didn't think of that one. Shut up... damn fans..."

Surely you should realise by now that the answer to any inconsistency is 'Wibbly-wobbly-timey-wimey'

"Most people think that time is a straight line of cause to effect, when acctually it is more like a big ball of wibbly wobbly timey wimey... ...stuff." Explains everything, time isn't just cause and effect with time travel, it is far more complicated than that. Also Amy, Rory and the Doctor are at the eye of the storm (the Doctor says this in the Big Bang) and that was why they were still there and also therefore explains why Amy could exist when her parents never existed.

If you have a problem with the explaination then why the heck are you watching a show about time travel!?

But you were okay about the ring? And the Saturnynians? And Rory's image in the picture left in Amelia's house? It was a sci-fi thing. Whatever was erased still left all the effects around it - like when the Doctor points out that they still call the duck pond a duck pond, even though the ducks have long-since left the pond (which means it should be called a pond instead, but wasn't).

Does anyone else think the title of this thread would make a great episode title?

Moffat's sort of answered this (well commented on it, he hasn't really explained it!)
"She remained as an anomaly - which we know happens, cos Amy survived her parents erasure."

Big holes were being ripped in causality, causality wasn't being rewritten.

A duck pond is a duck pond even if it doesn't have any ducks.
An Amy Pond is an Amy Pond even if it doesn't have any parents.

Eventually, as we saw, everything else collapsed too, and even little Amelia disappeared, making Amy even more of an anomaly, at the heart of the storm.

Being time travellers probably helped them all weather the storm of such disruptions.

I love the way that fans of Dr Who discuss in great detail paradoxes, plot holes and imposibilities in the series but at the same ignore the fact that its Time Travel science fiction and therefore ANYTHING is possible. Its set in a environment where all know laws of physics can be bent or even broken.

Not quite, the world is based on a simmilar set of laws as ours - such as in th Who universe space and time travel are possible and due to time travel being possible there are consequences for traveling in time - the paradoxes, "plot holes" and "impossibilities" you mention but on the whole I agree with what your saying.

But - if Amy popped out of existence it wouldn't be in keeping with the rules of the Dr Who universe when it came to the crack.

If people's actions were erased when they were sucked into the crack then:

1) Amy and the doctor would not have made it through the forest of the weeping angels as the soldiers were sucked into the crack.

2) Amy would probably have been killed by Prisoner Zero as the Doctor wouldn't have been there to save her.

All that seems to happen is that people forget you and make up some other story about how they got to where they are.

I asked a polite question and explained that I don't have the series or the DW confs for it recorded - I just wanted to know if it had been specifically explained or not, I didn't say that I couldn't write it off as artistic licence.

Thank you to those who gave polite replies.

FarStanley - thanks, decent suggestion.

Justine - thanks. I recall that Amy remembered the Clerics in the Forest after traveling in the Tardis and the Doctor said it was because that had altered her - (though it didn't stop her forgetting Rory).

RainbowFire - thanks. The idea that she's "special" in her own right is one option (though the disappearing parents happened pre-Tardis)

Seb - cheers. I'm not really okay with all of those things - in fact, I was thinking of what had or hadn't been erased in the series and the photo - also pre-Tardis - was something I had in mind. It seemed that only certain things relating to Amelia were not erased and I just thought I shoud check if Amelia's situation had been explained as being "XYZ" before going any further with the idea.

JohnnyS - thanks - I like that first line, nicely worded. Again, the parents went pre-Tardis so not really involved. The "ducks" - I thought that only those specific ducks vanshed - not all ducks everywhere - so they'd remember that ducks used the duck-pond (like persons vanishing - you'd still remember that there are people)

Butterflyy - thanks loads - an explaination from Moffat is what I was hoping for (if it hadn't been directly explained in the show). It shows that he aware that this was a paradox when he wrote it.

So far, so good, however it still doesn't explain how River could have existed prior to the universe reboot in the Big Bang, considering that Rory was killed/erased by the crack prior to the wedding, i.e. River couldn't have been conceived in the first place.

Ah, but River/Melody was conceived on their wedding night - so after the Universe reset.

It all depends upon whether the reset is a gigantic wall in the way of time-travel and so it impossible to travel to a time before it or whether it is just another moment in time. If it is a simple moment in time then it's feasible for River to travel back to before the reset.

Certainly makes my head hurt.

Because although it hadn't happened yet-it would happen. The whole mop Fez sonic crazyness of the S5 finale fudged the lines of that quite spectacularly.

This series it has been played with even more-what with the two Doctors, (older/younger) and the invitation to an event that had not happened yet, plus another version of himself-all very timey wimey.

I don't mind it, I love Terminator - I love paradoxes.

I just hope its is kept consistent, so we can figure it out-not be cheated by the result, if that makes sense.

Perhaps if that universe hadn't ended they would have got Rory back and River would still have been conceived.

River herself is different - she travels time and space too, so her outcome was probably safe due to that.

Remember, she had a blank diary, but still remembered to give it to Amy on her wedding day to remember the Doctor back... She's Human+, so is probably a fixed point in time.

So, River from a post-Big Bang universe travels back in time to a pre-Big Bang universe where she couldn't/wouldn't exist?

How could a Big Bang be "a simple moment in time" when it was made clear that those two universes cannot be crossed (only by the Doctor - and only because Amy remembered him)?

I think I just found the reason for the crack - the "two parts of time and space that should never have met": River crossed into the "wrong" universe