One of the few questions that remains is about the so-called "Five Principal Exceptions to Gamp's Law of Elemental Transfiguration." As stated in the novels, there are five things that cannot be conjured or, I think, made via transfiguration. In the novels, only one is explicitly named, leaving four more for me to guess at. What could they possibly be? I've been over and over it and come up with a few possibilities for the Five Exceptions:
FoodNaturally, as this is the one that is discussed in the Deathly Hallows:
"My mother," said Ron one night, as they sat in the tent on a riverbank in Wales, "can make good food appear out of thin air." [...]
"Your mother can't produce food out of thin air," said Hermionie. "No one can. Food is the first of the Five Principal Exceptions to Gump's Law of Elemental Transfigur-"
"Oh, speak English, can't you?" Ron said [...]
"It's impossible to make good food out of nothing! You can Summon it if you know where it is, you can transform it, you can increase the quantity if you've already got some -"
The food problem is also mentioned later in the same book, when Neville is talking about the Room of Requirements. The Room can supply everything they need, except food. This exception makes a few other things clear, like why house elves are usually in the kitchen and Sirius Black resorted to eating rats when he was hiding in a cave near Hogsmeade. (Although it doesn't make it clear why everyone just doesn't carry around a few crumbs of bread or something, if you can magically "increase the quantity" of food, and the implications of the "you can transform it" line is unclear.)
This critical passage gives us some clues for what the others may be. We now know what sort of "traces" the remaining four Exceptions will leave in the wizarding world. We need to look for things that seem rare or unique, or that have seemingly unnecessary economies. From these criteria, there are a few that are evident from simple logic.
Metals or elementsThis one is the easiest. There are two possibilities for a wizard currency: the currency itself is heavily protected with charms such that any forgeries are detectable, or the currency is made out of a substance that cannot be created magically. In Rowling's universe, the currency is made of metals:
Griphook unlocked the door [...] Harry gasped. Inside were mounds of gold coins. Columns of silver. Heaps of little bronze Knuts.
"All yours," smiled Hagrid. [...]
"The gold ones are Galleons," he explained. "Seventeen silver Sickles to a Galleon and twenty-nine Knuts to a Sickle..."
Each of these elements (gold, silver, copper, and others) has to be impossible to create permanently, or else there is a constant danger of forgeries that threatens the wizarding world's economic system. The latter is quite clearly not the case: at no point in the novels is it ever suggested that anyone be suspicious of any money they are given. (The same seems to apply to gemstones, too!)
The exception here is leprechaun gold, which evidently has the same properties of regular gold currency except that it disappears after a period of time. We are introduced to leprechaun gold in The Goblet of Fire, where Ron pays Harry in leprechaun gold, gathered from the Irish Quidditch mascots. Evidently it's not common knowledge that leprechaun gold is fake (probably because leprechauns aren't native to Great Britain!) Ludo Bagman, on the other hand, knowingly pays of his gambling debts with leprechaun gold. In the Deathly Hallows, a bank goblin is overheard muttering to himself, "Leprechaun gold" while examining a Galleon - Goblins, a race that is skilled with metals, seem to have little trouble telling them apart.
Thus, wizards themselves cannot create gold from nothing, and even magical creatures like leprechauns cannot make permanent gold.
There is just one potential catch to this theory: the Philosopher's Stone.
The ancient study of alchemy is concerned with making the Philosopher's Stone, a legendary substance with astonishing powers. The stone will transform any metal into pure gold. It also produces the elixir of life, which will make the drinker immortal.
The Philosopher's Stone is, understandably, an extremely rare and valuable object because it can do something that no other magic can do: create gold. The proof of metals or elements being one of the Exceptions hinges on allowing the Stone to be the singular exception to the Exceptions. This is a bit easier to swallow when you realize the Stone doesn't make gold from thin air, but rather transforms another metal into gold. Which is keeping in the spirit of the Exceptions - you need some metal to start with!
This one is a bit trickier, but it seems to make sense in the context of the novels and films. I think there is evidence to suggest that wizards cannot transfigure or create true living beings - or, at the very least, cannot create magical beings, which includes humans.
At several points all throughout the novels, we are shown teachers or students transfiguring objects into animals, or vice versa. We are never given many clues, however, about whether these transfigured animal are persistent. If one allows evidence from the films to be presented, we can assume that creatures created in this way are not real or persistent creatures. A good example is when Hermione uses the avis spell to conjure birds, followed by the oppugno spell which makes them attack Ron. The conjured birds disappear in a puff of feathers when they collide with a door, rather than falling dead upon the floor. Happily, the issue of conjuration is solved by Rowling herself in an interview:
Something that you conjure out of thin air will not last. This is a rule I set down for myself early on.
The second example from the movies happens to be one of my favourite scenes. This scene doesn't exist in the novels, but it makes a very poignant addition. This is the scene in which Slughorn tells Harry about the day Lily died, and it gives us a clue about the nature of transfiguration:
Even though the fish lives for (likely) several years after Lily first transfigured it, it seems to only persist while the caster remains alive. (This property of magic spells is fairly well-respected. For example, the moment Dumbledore died, the immobilization spell he had cast on Harry is removed.)
I'm a bit uncomfortable taking evidence from the films over the novels, but the novels don't have a lot to go on. I can quite confidently say that, based on the novels, one probably cannot transfigure a magical beast. If that were so, couldn't a wizard transfigure an object into, say, a unicorn, to collect the valuable tail hair or horn? Couldn't a wizard make clones of other wizards (or themselves)? Couldn't a wizard use magic to acquire rare, valuable plants? We know that Hogwarts has extensive greenhouses; why go through that trouble if one could just magic plants into existence? Why breed magical creatures if you could just transfigure a rock into a phoenix? Many potions require rare and expensive ingredients that originate from animals or plants... so these things must be rare for a reason.
A poor transfiguration spell will give you an object that acts like its original, (e.g. the hedgehog turned pincushion that cowers from pins)Furthermore, there appears to be a spell to transform an object or creature back to its original state. The original thing survives, even if its appearance and behavior are altered. We see plenty of examples of magic creating life (animals such as birds, plant life such as flowers), but I would bet that such "life" isn't really life at all, and that it's only the strength of the magic that makes it behave or look as if it were alive.
In Rowling's universe, the soul is a thing that actually exists, separate from the body.
"You can exist without your soul, you know, as long as your brain and heart are still working. But you'll have no sense of self anymore, no memory, no...anything. There's no chance at all of recovery. You'll just -- exist. As an empty shell. And your soul is gone forever...lost."
The soul being separate from the body is the fundamental fact underlying the Horcrux; extremely dark magic that can allow a wizard to live on even if their body is destroyed. Creating a Horcrux involves ripping one's soul into two and concealing the second piece of soul in an object. In Voldermort's case, he created seven Horcruxes - that is, his soul was contained in seven external objects (and even other living beings), in addition to the fragment that was in his body. This left his soul extremely unstable, and were all the Horcruxes destroyed, Voldermort's soul would cease to be - he would not be dead, but would rather exist in Limbo.
"But even if we wreck the thing it lives in," said Ron, "why can't the bit of soul in it just go and live in something else?"
"Because a Horcrux is the complete opposite of a human being."
Seeing that Harry and Ron looked thoroughly confused, Hermione hurried on, "Look, if I picked up a sword right now, Ron, and ran you through with it, I wouldn't damage your soul at all."
"Which would be a real comfort to me, I'm sure," said Ron.
"It should be, actually! But my point is that whatever happens to your body, your soul will survive, untouched," said Hermione. "But it's the other way around with a Horcrux. The fragment of soul inside it depends on its container, its enchanted body, for survival. It can't exist without it."
A soul is a singular, unique object that (usually) exists intact. It is your essence - your body drained of soul can live, but "you" are gone. A fragmented soul can only be repaired with an "excruciating painful" process that involved real remorse for the acts that tore it apart.
Ghosts are the "imprint of a departed soul." A ghost cannot be destroyed, transfigured, duplicated, or perform any magic of their own, and are (mostly) incapable of interacting with the physical world; one likely needs a body to do that. They also know nothing of what happens after death; they have chosen to stay in the mortal world as undead, rather than "moving on."
As is stated several times in the novels, it is impossible to bring someone [IE a soul] back from the dead. We are introduced to several forms of magic that can appear to bring someone back from the dead, but most of them provide only imitations or memories (such as priori incantatem), and none truly bring someone back to life. A good example is the resurrection stone (one of the deathly hallows) which can recall an existing soul from death, with a catch:
"Yet she was sad and cold, seperated from him as by a veil. Though she had returned to the mortal world, she did not truly belong there and suffered."
Finally, one cannot create a soul to reside in an "empty" body - otherwise, some dark wizard would use that magic to create an army. (Grindelwald thought the resurrection stone could be used for this purpose)
Presumably, the only way to create a new soul is through the usual, er, tried and true methods. Other than that, souls seem to be a likely candidate for one of the Exceptions.
The last Exception has proven to be a challenge. I am quite confident that the three items I picked follow in the spirit of the sort of things that would be an exception to a "Law of Elemental Transfiguration." Things that are decidedly physical (though that gets a little shaky for souls) which still cannot be conjured or transfigured, no matter how powerful or learned a wizard is.
I've been over and over it, and the only plausible fifth Exception that makes sense would be water. Water is necessary for the body, just like food. Having conjured water disappear after you have drank it would be problematic, to say the least!
I propose that the reason wizards can seemingly conjure water out of thin air is because of this property:
...you can increase the quantity if you've already got some...
Water is one of the few substances that is ever-present. There is always moisture in the air, not to mention the moisture in one's body! If all you need is a small amount that can be duplicated, then one would never run into a situation where the inability to conjure it from thin air was a problem.
The "rules" of the Exceptions likely vary from Exception to Exception - I proposed that ghosts, gold and souls can't be duplicated, but we have been told that food can. Perhaps some Exceptions have stronger limitations than others.
I've mulled over a few other possibilities, but rejected them for various reasons. There are a few ideas that seem likely, except that they aren't substances. Throughout the series, for example, Rowling makes a very big deal about love. In the Half-Blood Prince, professor Slughorn states quite clearly that love is something that cannot be created:
"Amortentia doesn't really create love, of course. It is impossible to manufacture or imitate love. No, this will simply create a powerful infatuation or obsession."
Alas, love isn't a physical substance that can be conjured or transfigured, so I had to abandon that idea. The same goes for concepts like weather.
There were some objects that I thought had "unnecessary economies" surrounding them: things like clothing, houses, books, furniture, etc. I decided it is likely that a wizard could create these things via transfiguration, but that it is so incredibly complex that it's just easier to buy the damn things.
I suspect it is a similar story with wands. Clearly, a wizard cannot simply conjure a wand, or turn any old stick into a wand. It appears you need both years of training in wandlore (such that there are only a handful of wandmakers in Europe) and a magically powerful core component. Stemming from my argument about the inability to transform magically powerful creatures, it is likely that one wouldn't be able to create the magically powerful components (such as dragon heart string, unicorn tail hair, veela hair, or phoenix feathers) that are required in wands. I don't think wands themselves are an Exception, just that they require skilled and powerful workmanship.
If you've made it this far, do you have any plausible ideas?