Gamp's Law of Elemental Transfiguration

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 does not seem to be an exception, as birds can be created using the spell Avis, and flowers with Orchideous. However, It´s 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. 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.

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 can´t 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 resembles the charm or spell used by the house-elves, which transfer food from one plate to another counterpart above in the great hall. Molly Weasley also appears to conjure 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 can't be conjured; but since animals can be conjured (such as when McGonagall transformed her desk into a pig one time), one may theroetically take meat from the animal.