Hm… Kinda wonder if that is not Celestia, then how come moments later she just casually drops in saying “That is because she IS a princess.” as if continuing the discussion from the ether.
Of course, being an “all mighty”, “omniscient”, or “omnipotent” being it could just have telegraphed what was happening to Celestia at the same time as it was having this conversation with Twilight. A conversation where it was holding the very book Celestia and Luna were holding at the very beginning of Season 3. So, Celestia and Tree in cahoots? Wouldn’t put it past them…

And then the very next Season we see the Tree in peril where it needed the elements back to recharge and fend off the plundervines. So, I guess that makes sense that it used the last of its main powers to bring Twilight into the ether, speak with this visage, and turn her into an alicorn.

@sonicfan
Yeah, that sounds about right. When the six Elements of Harmony were returned in the beginning of Season 4, it just made this chest, awaiting for an additional six “elements”, which when those were presented grew this castle with six (plus one) chairs and this map, and then mindlessly sent ponies to various corners of Equestria.

Wow..that…is actually totally plausible. Headcanon’d, sort if.  
That ’ I’ve watched you since that very first day’ line. Ive always felt it would be impossible for celestia to get all those images of twilights life unless she placed a stalker spell on her. But on the other hand doesnt Princess Luna have a similar glow in the dream realm. Just not as saturated a Celly’s.  
So i think twis ascension was a combination of the efforts of the Tree AND Celestia. Maybe Celestia has worked out a way to sense the tree so that she can be there at the moment Twilight is ready for ascension. As for ‘very first day’… ehhh. I guess Celestia totally put a stalker spell.

Being manipulated, even in one of her defining moments.

@Josh103  
For a while though, Celestia being responsible for the transformation seemed to be the most likely possibility. Due to what was known of Cadance’s ascension (which Celestia was also present for), it was clear that the Elements of Harmony were unrelated to the process, and the idea of the tree itself being a participant was not yet within the realm of consideration.

I always disliked the headcanon that it was Celestia. She was merely the witness.

Hmm… it might be possible. At the very least, if the tree itself is the source of the ascension (with the elements themselves being unnecessary), then Cadance’s backstory could fall in line with it.
 
If nothing else, there’s an extremely strong possibility that the tree is the source of that strange dimension that Twilight and Cadance visited.

@Background Pony #DB50  
Is either that or it’s a different dimension.

Probably not, because celly isn’t sparkling like a vampire.

Holy crap, that’s actually VERY plausible.

@Background Pony #A010  
Yeah, because the bright purple starburst in the sky totally wasn’t a beacon to where Twilight was. Also, Celestia discusses with Luna when the Crystal Empire returned regarding Twilight being ready. That readiness was referring to Twilight having the right knowledge and ability to solve Starswirl’s unfinished spell. Celestia sent Starswirl’s unfinished spell to Twilight. Celestia knew about Twilight becoming an alicorn because she was preparing Twilight to ascend into an alicorn.
 
Also, Occam’s razor is only applicable to science, once you throw sapient life into the equation, then things get far too complicated to apply Occam’s razor theory to.

@sonicfan  
Then Flurry Heart happened.
 
Anyway, if that wan’t the real Celestia, how would Celestia know about Twilight becoming an alicorn and when and where to show up for it? Thinking it was the Tree, which was at the nadir of it’s power and only recently gained the ability to directly act or manifest just makes the whole scenario more complex. I have to call Occam’s Razor on this theory.

Intresting

@SD50-2  
It isn’t until after the Mean Six episode that we see the Tree behaving as a sapient A.I. rather than the preprogrammed artifact of protection which it had previously operated as.
 
I see it as taking a mechanism and using another’s programming to learn. An A.I. simulation which through the absorption of other sapient creatures in order to become more than her programming. Like an update to a program, or an upgrade to the firmware.
 
The Mean Six episode had something within the Mean Six which had the right stuff to propel the Tree into the realm of sapience and not at all in episodes prior to that.

@SD50-2  
I wouldn’t see it that way. I see it as more of a restoration of power to the Tree’s functionality. Think of it in terms of a cell phone. If a cell phone doesn’t get recharged before the battery reaches a certain percentage, then certain functionalities, apps, and programs may become unavailable due to insufficient power.
 
That was why it was important to return the elements is because the Tree’s power had dropped to such a degree that the protective functionality which it had provided before had dropped to such a level that the protective functionality was dropped/suspended because it didn’t have enough power to fight against invasive plant species such as the plunder vines. Once the elements were restored to the tree, (I.e., power restored) then the Tree was able to restore the protective functionalities that had either been suspended or turned off due to the restored power. Once the protective functionality had been restored, then it was able to eliminate dangerous and invasive things such as the plundervine.

@sonicfan  
Is it possible that returning the elements to the tree allowed for it to gain sapience?

Except that it was clearly stated that alicornism must be achieved by performing a magic which had never been done before. That’s why we don’t have an alicorn of omelettes, or an alicorn of cupcakes, or an alicorn of roasted grilled corn. Otherwise why wouldn’t the Tree turn its/her(?) parents the Equestrian Pillars into alicorns and then the rest of the pony tribes? Because doing something like that would reduce animosity and interpersonal friction by giving them access to the powers of all three tribes, rather than the one to which they’re born into.
 
I think that prior to a certain point, the Tree was more like a magical artifact which was programmed to respond to different situations. It was only after a certain point had been reached that it became sapient. (I’m looking at the Mean Six episode.)
 
Also, it was Twilight performing a magic which had never been done before, that was responsible for her becoming an alicorn. The reason why the Elements reacted the way they did is because of her bonds with her friends and the magic which connected them all together. Twilight’s magic is why she ascended. The magic of friendship employed the Elements to the end of ascending Twilight into an alicorn because of her friendship with her fellow Element Bearers.

@Background Pony #17D5  
What I meant was that it’s common knowledge within the fandom that what triggered Twilight’s ascension was some inner magic related to the EoH. Celestia was the one who saw in the filly a potential successor (according to Faust) and guided her. People usually say Celestia gave Twilight wings in a tongue-in-cheek way, because she certainly saw to it that Twilight’s entire life would lead up to that moment.

Not overly surprising.

@Background Pony #71DB  
@blizzard64
 
Mind blown, maybe the tree actually did turn twilight into an Alicorn, the tree show itself as the one who you admired. If you think of it, it’s kinda weird that P.Celestia would have each and every scene from twiligt past time Season 1 until 3. P. Celestia know that twilight will turn into an alicorn if she complete every lesson that she give it to her or maybe the lesson is from the tree of harmony itself.

Hmmm interesting. it make you think

Well since I’ve saw this, I’ll never the season 3 finale the same way again.

@blizzard64  
I believe it was the actual Celestia in there and she somehow has access to that realm, maybe even the other alicorns aswell. The show runners at that time clearly meant it to be Celestia talking Twilight through the transformation, but if they want to retcon it now and say it was the tree, eh what the hell, it would probably make more sense.

That’s what happened with The Elements But the Tree came after Season 4

@Background Pony #71DB  
Do you think it was Princess Celestia who sang?  
or  
Was the Tree of Harmony who became the Princess Celestia to talk to Twilight?

What. That’s literally what happened. The elements blast Twilight into the ether and then the magic comes out of Twilight, envelops her and she ascends. That was never even disputed. Celestia is there and sings a song but she never cast anything, and it’s ridiculous to think Celestia can turn ponies into alicorns.