Gamp's Law of Elemental Transfiguration

"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—... 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 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.

The formulation of Gamp's Law has not been stated, but food being one of its Principal Exceptions means that it cannot be created from nothing. Therefore, it can be reasonably inferred that Gamp's Law relates in some way to magic that creates something from nothing. It can also be inferred that the other four exceptions are other categories of substance which cannot be created from nothing.

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.

History

McGonagall summoned food from elsewhere, as when conjured a never ending platter of sandwiches to Snape's office from the Hogwarts kitchens; increased, as Hagrid did by using the Engorgement Charm on pumpkins; or transformed as Molly Weasley did when cooking. As one of the Principal Exceptions to Gamp's Law of Elemental Transfiguration, food cannot be "made from thin air", but 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.

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.
• The series appears to break one of these laws early on. In Harry Potter and the Chamber of Secrets, McGonagall appears to conjure a platter of sandwiches and a jug of Pumpkin juice out of thin air when Harry and Ron arrive late; however, she may have simply apparated the food from the kitchen similar to the way the house-elves make the food magically appear for feasts.

Appearances

• Harry Potter and the Deathly Hallows (First mentioned)
• Harry Potter: Hogwarts Mystery (mentioned only)