The next important developmental step in the philosophy of nature was the result of Socrates' interest in virtue! The modern concept of virtue as moral correctness originates with Socrates. In order to formulate that concept, it was necessary to rise to a high level of abstraction. It is very characteristic that European philosophy began to sharpen its theoretical tools on problems connected with ethics. It was precisely on the terrain of ethics that the concept of essence first appeared. Socrates asked, for example: What is justice? Wanting to distinguish justice from related virtues, he sought those traits which were their essence and not just those which happen to be associated with justice. An awareness of the difference between the constitutive traits, which were its essence, and the accidental traits, which only happened to be associated with the given concept, was a major achievement of Greek philosophy. It produced Plato and has had an impact on all of European thought.