Harry's POV
Going back to the room of requirements, Harry put aside the physics book as he started a few days ago reading once again books about a subject he hasn't read since the beginning of the year- alchemy.
The reason he stopped reading about it was not only because of the time limit he had to find the cause to Astoria's sickness, but also because of disinterest.
After reading that alchemy isn't actually about transmutations, but about the levels of change the body and magic can go throughout a person's life, and understanding the kind of change he wanted his body to go through would take time and effort, as he didn't want to only become a Metamorphmagus who can change their body shape partly or animagus who can transform into an animal, he didn't even want to become a combination, being able to change partially or fully into any animal didn't reach the top of his idea for a perfect body, no, he wanted a full control over his body, down to the cells and his DNA.
It was only now, that his first step was over, that he managed to create spells and AI whose purpose is decoding the DNA, and that he managed to get the Greengrass to not only support him financially (as he might have money, but he knows 'you should never pay for something someone else offer to'), but also with books about rituals and transformations magic, not to mention getting Metamorphmagus' DNA and even help him get a Maledictus, with his sight on one who would become well known in the future, Nagini, that he could focus on the subject.
So now, when he has to wait for the books to come he can focus on what's to come after changing his body, his magic's second transmutation, fire, or as he preferred to think about it - plasma
According to the books, while the first and second states are about having as much magical energy as possible, filling your 'magical core' (he still hasn't found anything like that in his body, and waited for the solid stage for more information) with gas so much that it becomes liquid and then filling it with liquid, with the second stage also teaching you control, the third stage is where individualities are starting to show up, where your magic is getting to a stage where things you are god at are getting better and the other things becoming unusable.
It both made sense and didn't at the same time.
It made sense as he could see the 'big shots' having specialties- Dumbledore and transfigurations, Voldemort and dark arts, the professors and their subject, each ones of the people who can fight the main fight has their own specialties and things those are almost the only thing you see them use, and the higher up they are, the less you see them use other kinds of magic.
Yet he can't understand why, as he only considered magic as energy till now, something that goes by the rules of science, he hasn't managed to find any reasonable explanation why specialties affect your magic so much so that as you gain the ability to go into specific higher magics, you lose your ability to perform regular kind of others.
It terrified him, he didn't want to lose that ability, he liked how diverse magic is, and even more then anything else, he liked that magic made sense, that his magic followed the rules of science almost always, and it didn't help that he kept being reminded about the 'almost'.
Patronus, the one magic he managed to do without the knowledge how it worked.
Yes, he has no idea how the spell worked or why, the only reason he managed to do it was that he learned it young, making it a non-accidental, accidental magic.
He understood the explanation the magical people gave to use it, but that, along with everything else they were taught in school felt like the greatest bullsh*t anyone ever created.
While he can admit words and wand movement can bring some results, he knew that without intent and real magical energy control it was just like teaching kids how to swim by throwing them into the water and watch them drown, while some might succeed, non would become Olympic swimmers. Not to mention that Harry found out by competing results, that by doing magic without the knowledge how it affects the world, especially if done wandlessly, use twice as much magical energy, making it easy to understand why even people who know wandless magic before school stop using it.
Knowing the third stage of magic is known as the purifying stage, and that he would have to sacrifice parts of his magical ability for it made him swear to find another way.