The two pre-Socrates philosophers Heraclitus and Parmenides who existed way back in around 600 B.C. both agreed that the world could be reduced in to one thing, both of their arguments are based on change although their point of view is the complete opposite.
Heraclitus believed and proposed that all is change. “No one can step twice in the same river, nor touch mortal substance twice in the same condition.” He proposed the concept of flux; he felt that it must apply not only to rivers but to all things including human souls. His philosophy consisted of “change is only constant in the world nothing will ever be the same as it was a moment ago.” Heraclitus thought that everything was made out of fire, because a fundamental property of the universe was that it was always changing and the only other thing that he could think about that was always changing was fire. Fire, then, became the uncaused source of change in the universe, and the incarnation of the will. To him, fire was god. Parmenides on the other hand couldn't disagree more, in fact, he thought that the entire idea of change was impossible and the world was basically a huge unmoving solid chunk of stuff. He then went ahead and used logic to disprove the possibility that anything can ever move. Be offering the theory that the entire universe consists of one thing which never changes, has no parts and can never be destroyed He calls that single thing “the one”. Parmenides proposed that change and movement was impossible “it’s only an illusion”. He argued that one must be motionless: if it moved, then it would not exist where it was before. Both philosophers had a difficult time trying to rescue eternal being from the flux of appearance and change.