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 governing the magical world. There are five Principal Exceptions to Gamp's Law, one of which is food.

It should be noted that while food cannot be outright created from nothing, it can be multiplied if one already has some food to multiply, it can be enlarged or the food can be summoned if one knows the approximate location and is fairly sure the food will still be there. It should also be noted that while food cannot be conjured, consumable liquids such as sauces and potable water can be. It should also be noted that this law is entirely pointless; since if you can imagine that there is food in the Hogwarts kitchen, then you can summon and multiply all of the food that you need.

History

In September 1997, after Ron commented that his mother could make good food out of thin air, Hermione stated that this was impossible, as food is one of the five Principal Exemptions to this law, but this only irritated Ron, who wanted her to "speak English", but was not satisfied by her explanation.

On 1 May, 1998, after Neville Longbottom noted that the one thing that the Room of Requirement did not seem to be able to provide was food, Ron commented that food was one of the five Principal Exceptions to this law, to "general astonishment".

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.
• According to W.O.M.B.A.T., it may or may not be possible to turn an animal into a human. 
• Although many things appear impossible to conjure, there is legislation in the wizarding world about what can and cannot be conjured. 

Appearances

• Harry Potter and the Deathly Hallows (First mentioned)