Definition:Philosophical Element/Quintessence

Definition
Quintessence was the fifth element postulated by the Pythagoreans, and was supposed to be the material out of which the heavens were made.

It was postulated in order to explain how the heavenly bodies were in constant motion, and never came to rest like everything else that could be seen in the universe.

Also see

 * Definition:Aether (Physics) (an attempt to revive the concept in order to explain action at a distance)