This idea was accepted by most of the philosophical schools of the time, including the Atomists.
Plato took quite a different approach and found that ideas, as noted, and saw idas as existing outside of human consciousness. Plato's doctrine of recollection holds that learning is the remembering of a wisdom that the soul enjoyed prior to its incarnation, another aspect of the idea that there are ideal forms "remembered" by the soul in this world, and this is actually a mythical statement of this view that neither reason nor the intelligible order that it reveals is alien to the human soul. The soul is seen as existing before life here on earth and as remembering the ideals it knew before birth. Protagoras would not have engaged in this sort of argument, jus as he avoided arguments about the existence of the gods as being outside of sensory experience.
3. Plato's ideas are similar to some of the Asian philosophies regarding the nature of life and the structure of the universe. The idea of a duality is found in many of these philosophies, and Plato was clearly a source for some of the teachings of Islam and related doctrines. The idea of an eternal realm is common in many religious doctrines and so can be seen as having some relationship to the Platonic view of eternal forms, though not in just the same way. Lao-Tzu contributed to the development of Taoism, seeing Tao...
Non-being is emptiness, or what is not, and it has as much significance as does being, the fullness of things, or what is. In this way, Lao-Tzu captures and reforms the earlier Chinese concept of Yin and Yang, the polarities running through all things. Duality links Plato to the Asian philosophies, though how they envision the duality of the world will differ.
4. The question of whether there is an absolute truth or all truths are merely relative in itself requires a clarification, for the real issue is whether truth can be perceived. There is an absolute truth almost by definition, but the ability to see that truth is governed by limitations on perception and by other forces that can make truth relative to the individual doing to seeking. This view is probably closest to the Sophists. The Sophists considered the nature of law and whether law could be viewed as something objective, a scientific certainty to be applied to the world. Essentially, the Sophists found that there was no way to know whether there could be such a law or not and that therefore there was no reason to seek it. The Sophists saw themselves as enlightened when compared to the superstitious Greeks who had gone before, and they thus no longer believed in the gods as the source of a law for mankind.
