Empedocles (c. 490 – c. 430 BC) was a Greek pre-Socratic philosopher. He thought himself to be a god among men, and as legend goes, jumped into a volcano to prove that he was immortal; needless to say he died.
He is known as the person to come up with cosmogenic theory of the four Classical elements. This essentially was the belief that all things were made up of the elements, earth fire air and water. The elements themselves believed not to change; just moving around and combining with each other.
He also proposed forces called Love and Strife which would act as forces to bring about the mixture and separation of the elements. He thought them to be constantly at battle with one another:
- Love, responsible for bringing the elements together to make up things around us, as well as human emotion (this force of love is actually what caused humans to feel sexual attraction towards each other)
- Strife, continually trying to separate the elements apart and break them down (driving people away from each other and creating problems)
He thought of the result of this constant battle to be the changing world around us.
Empedocles is also credited with the first comprehensive theory of light and vision. He proposed the idea that we see objects because light streams out of our eyes and touches them. Although not correct, this became the foundation on which later Greek philosophers and mathematicians, such as Euclid, based some of the most important theories on light, vision and optics.
Sources: Philosophize This! (http://www.philosophizethis.org) | Wikipedia (http://www.wikipedia.com) | Internet Encyclopedia of Philosophy (http://www.iep.utm.edu) | Britannica (http://www.britannica.com/biography)