Impure elements

“You may have broken the hot and dry, but the hot and wet and cold and wet are joined
with it. There are no pure elements at the surface of the four worlds, but the isolated cold
and dry will use its great influence to disturb the world’s harmony. Earth born of fire, use
your great fusion to reinforce your meaning and strike the destroyer of the elements!!”

There were four elements.

In the largescale ceremonial magic used by the Golden cabal, you could not exclude any
of those four even if you only wished to use the one.

In a technical sense, there were no pure elements in this world.

For example, fire always contained some trace amounts of water, wind, and earth.

Trying to remove that margin of error would be the same as forcibly removing electrons
or protons from stable atoms or molecules.

-Shinyaku Toaru Majutsu no Index Volume 21 Chapter 3 Part 16