In response to Parmenides, Anaxagoras worked out the astonishing theory that all physical change is nothing more than an emerging into view of something previously latent. Thus, we have no need to speak about what is not, but only about what we do not yet see.

The interpretation and assessment of Anaxagoras put forward here differ substantially from what is found in most contemporary histories of philosophy, in at least three respects. I believe Anaxagoras' theory is quite independent of Zeno, and that Zeno, in fact, criticized him. I also think that Anaxagoras did not criticize and modify Empedocles' theory of elements, but represents a more primitive stage of response to Parmenides than Empedocles. Moreover, my interpretation of his theory of matter is not quite the same as any other that I have read. These are all controversial positions, which cannot be defended in detail here.

Anaxagoras

Anaxagoras began his book with a striking affirmation that at once made clear his opposition to Parmenides:

Parmenides had agreed that what is is invariant in time, so that only ‘it is,’ and not ‘it was’ or ‘it will be,’ is correct, and that it is uninterrupted in space by any interval or change of density.