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Spoilers for
Changes ]
That aside, I think you're totally right about the Necromantic Thaumaturgy at Evocation speed -- I wouldn't let someone set up and perform a long ritual to handle this kind of thing (like with Biomancy) while the patient is bleeding out. Given the circumstances, I don't think anyone other than a Necromancer COULD have saved that thug's life. Even if you happened to have a White Council Master of Biomancy (like Injun Joe) right on hand with sufficient lore for the purpose, it would have taken him a few exchanges to run the ritual -- it was vital that Kumori could step up and stop him from dying RIGHT THEN before he could bleed out.
Not that this has much to do with the mechanics of the RPG, but I'd bet that the only fundamental difference between evocation magic and thaumaturgy is the caster's own ability to perform one on the fly and not the other. By this, I don't mean to just restate the definitions of evocation and thaumaturgy; I mean that I think there is
literally no real difference between an evocation spell and a thaumaturgical spell, other than the caster's own proficiency at casting the spell in question.
Harry says over and over again that magic is in the mind.
In Changes, he even performs a summoning ritual entirely within his own imagination, and the spell works. The binding part of the spell was probably about as strong as a Kleenex, it still technically existed, to some degree.
I'd bet that if Harry practiced such a mental ritual over and over and over again, for years, he could effectively turn it into a form of evocation magic for himself.
I'd also bet that this is essentially the difference between the Senior Council and the younger wizards. The SC has so much practice and skill that they can snap their fingers and throw up a spell that would take Harry all day to perform, if he could manage it at all. And as their skill with those kinds of spells increased, new forms of thaumaturgy came into their reach-- things they probably couldn't even imagine when they were younger, much less have any hope of casting.
I started thinking this was probably the case when Harry's skill with Little Chicago jumped so much between
Proven Guilty and
White Night. In PG, he had to prepare for hours before he felt ready to use Little Chicago, and even then he wasn't sure about his chances. In WN, though, after teaching Molly for a year, it only took him fifteen minutes to get ready, and he had no worries about successfully casting the spell. I figure, in a few more years, Harry might be able to perform the spell immediately. It's also entirely within the realm of possibility for Harry to gradually remove the trappings of the ritual as he continues to practice, replacing them with their mental counterparts. Once he had removed all of the objects, he would have effectively turned a thaumaturgical spell into an evocation spell.
The same mental techniques that he used to prepare himself for LC probably carried over to some of his other spells, too-- which means that Harry was bringing a whole group of spells within reach of becoming evocation magic for him. And if Harry's skill could increase that much in only a few years, it's hard to even imagine how much the Senior Council's level of skill could have increased beyond a wizard's baseline. They've each had hundreds of years to practice, re-think what they know, and build on new insights.
Admittedly, though, Harry's increase in skill was largely due to taking Molly on as his apprentice. By teaching her, Harry was forced to go back and re-think things that he already knew, seeing them with a deeper understanding than he had the first time through. And Molly's natural talents lay in very different areas than Harry's do, so he had to practice with things he'd never been good at before, until he could cast those kinds of spells with a halfway-decent amount of skill. He probably wouldn't have made such a huge effort in those areas if he hadn't been teaching Molly. I'd imagine that most wizards don't have that kind of impetus to keep getting better, year after year; at least, not on a daily basis, like Harry's had lately. So, even some of the older wizards wouldn't necessarily have a huge advantage of skill over some of the younger ones.
People like the Senior Council members, though, are probably some of the more well-motivated types. It seems possible that their skills could have been increasing steadily for the last three hundred years or more.