[Spoilers MAIN] My thoughts on Magic in A Song of Ice and Fire
One of my favorite ASOIAFYouTubers, In Deep Geek, has numerous times voiced the notion that Qyburn uses "the science magic" to bring Gregor back to life. But I think that idea is actually erroneous, as it does not take the existing "laws of magic" into consideration.
First of all, I want to establish my opinion that in the world of A Song of Ice and Fire, gods do not exist. Nevertheless, magic is quite real, as we have witnessed it on multiple occasions in the series. But then a question arises: what kind of magic exists in this world?
To answer it, I will refer to the title of the series, A Song of Ice and Fire. Hence, I'm led to believe that there are only two main types of magic, which are: fire magic and ice magic. But then, what about shadow binding and blood magic?
Shadow binding is not a type of magic by itself but a subset of fire magic. Melisandre states: " There are no shadows in the dark. Shadows are the servants of the light." George never reveals much about magic. One reason for that is his unwillingness to over-explain and make bland this crucial element of the story. The other one is, I would say, the in-world explanation. No one actually knows what magic is. We never see any scientific study of magic. The Citadel shies away from anything related to magic. The only maesters who try to apply any form of scientific methodology to unraveling magic are Marwyn and Qyburn. The one of the most powerful mages of the ASOIAFworld considers magic the gift of god, which, as stated above, is not the case. Also, considering that in the last 150 years magic wasn't that potent, people don't give too much credit to magic at all. Therefore, magic is convoluted and subdivided into categories that are actually one type of certain magic, either fire or ice magic.
Blood magic, on the other hand, is not magic at all, but the resource that all kinds of magic require to operate. In other fantasy series, magic is often created from some kind of mystical energy already present in the world. In The Witcher, Yennefer explains to Ciri that the source of magic is the energy in the world that they exploit to create spells. In A Song of Ice and Fire, sacrifice is this mystical energy. Blood is the required component for magic to work. Daenerys kills Mirri Maz Duur to bring dragons back to life, Bran consumes Jojen's blood to strengthen his magic, Shiera Seastar bathes in blood to keep her youth, and so on.
So, there's only fire and ice magic; no "science magic" is present in the series. But in themselves, they are two opposite sides of the same spectrum of magic. Unfortunately, despite knowing at least something about fire magic, George hasn't revealed much about ice magic, as it's mostly reserved for the Others. But we know for sure that they both perform quite a similar miracle, which is the resurrection of the dead. There is where the major difference between the two types of magic comes from.
People resurrected by fire magic are fixated on the last and most fervent thought they had. In the books, there are two prominent figures that we know a lot about, and one who will be resurrected in the future installment. The first is Beric Dondarrion, who was killed during the ambush by The Mountain. There isn't any written evidence of what he was thinking during that time, but based on his subsequent actions, I would assume that he believed with his whole heart that he was meting out justice and serving King Robert. The second resurrected character is obviously Catelyn, and thanks to being in all of the first three books, we have a lot of evidence regarding her desires. Back in A Clash of Kings, she tells Brienne: "I want them all dead, Brienne. Theon Greyjoy first, then Jaime Lannister and Cersei and the Imp, every one, every one." Especially in her last moments, she was carried away with thoughts of revenge. She killed Jinglebell in an act of revenge. Post- resurrection, she cares about nothing but vengeance. I infer that Jon will have a similar arc to Catelyn in The Winds of Winter. Nevertheless, all of them retain agency, and despite being influenced by their most recent and fervent desires, they continue to act of their own volition.
On the other hand, ice magic can also bring people back to life, but from what is present in the books, there is not one instance of them having agency whatsoever. The Others bring back a lot of people from the dead, to the extent that they have a whole army capable of storming a well-fortified company of the Night's Watch. The other character that is fairly evidently brought back with ice magic is Coldhands. Although he's capable of speaking and making his own decisions, he's still bound to Bloodraven 's will. He has no volition of his own, that we know of.
To return to the beginning, I believe that Robert Strong is resurrected by ice magic. He has no apparent features of Gregor, save his massive build, and his only purpose is to serve. Qyburn was long experimenting on people, and I can imagine that he somehow learned ice magic.
I don't have any clue as to how Greenseer magic fits into this framework other than this queer observation of mine. Fire is associated with the color red, but burning fire is more yellowish-orange, and if yellow and blue are mixed together, we get green... (yeah, it makes little sense). But also, when Jojen and Meera first meet Bran, they swear fealty that goes: " We swear it by ice and fire ," which makes me think that Bran is really a weird combination of both.
I'd love to hear other opinions on this.