Gamp's Law of Elemental Transfiguration

Hermione: "Your mother can’t produce food out of thin air, no one can. Food is the first of the five Principal Exceptions to Gamp’s Law of Elemental Transfigura—"

Ron: "Oh, speak English, can’t you?"

Hermione: "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..."

— Hermione Granger and Ron Weasley on the exceptions to Gamp's Law

Gamp's Law of Elemental Transfiguration is a law of wizarding physics which states what powers magic has to create or destroy matter. There are five Principal Exceptions to Gamp's Law; some are food and love. Food may be multiplied once a real food object is actually in hand, but cannot be created from nothing. Love cannot be created; it can only be imitated through a Love Potion or the Imperius Curse, in which case it resembles an obsessive infatuation.

Life initially seems not to be an exception to Gamp's Law, as birds can be created using the spell Avis, and flowers with Orchideous. However, it is impossible to bring a dead person or animal back to life again.

The Philosopher's Stone does not create gold, but merely changes other substances into it. Leprechauns may create objects that look like gold or money, but which will, in time, change back to dead leaves or dirt; it is merely an illusion or transfiguration. Even Leprechaun gold will vanish into thin air after a few hours. The Geminio Curse may also cause the illusion of created gold, as was witnessed in the Lestrange Vault at Gringotts in 1998. However, this was a curse placed on the real, existing gold and would multiply any object it was cast upon, not necessarily gold, and are worthless in monetary values.

Behind the scenes

• Gamp's Law apparently uses the surname of the person who discovered it. Hesper Gamp, a witch married to Sirius Black II, might be that person or a relative of that person.
• Food cannot be conjured, but this is what Minerva McGonagall seems to do in Harry Potter and the Chamber of Secrets. However, it is most likely that she used a spell that can summon food from one place to another without travelling through the middling space. This may resemble the charm or spell used by the Hogwarts house-elves, which transfers food from one plate in the kitchens to its counterpart above in the Great Hall. Molly Weasley also appears to conjure a creamy sauce into a pan in Harry Potter and the Goblet of Fire. However, Gamp's law announces that you cannot create new food out of nothing, but you can conjure it if you know where it is.
• Food cannot be conjured; but since animals can be conjured (such as when McGonagall transformed her desk into a pig one time), one may theoretically take meat from the animal; however, the quality of that meat is debatable and could possibly provide magical side-effects such as splintered tongues.
• "Engorgio" allows any existing food to be enlarged, possibly feeding more people after enlargement.
• According to W.O.M.B.A.T., it may or may not be possible to turn an animal into a human. It also may be possible to make the inedible edible and not all objects can be transfigured into food.