Philosophical school agreed to have started with Parmenides of Elea in the 6th century bc. Its other members were Zeno, whose defence of the Parmenidean doctrine of the one indivisible and unchanging reality is the best-remembered work of the school (Zeno himself may have rejected both unity and plurality), and Melissus. The Eleatic principle is the view that the only real entities are those with causal powers.