Anaxagoras held that the objects of sense perception, both entities and qualities, were existents, and not relative to the percipient, and that they formed a continuum which observed the criteria of Parmenides' being. Birth, dissolution, growth and change of quality were explained in terms of combination and separation. the opposites were inseparable and infinite in degree, and the parts of the spectrum were one. the opposites were used to account for sense perception as well as for pleasure and pain. Since animals and plants are all product of the same natural process, they are essentially alike. Man lives in a world which has no purpose and no god, but, by means of observation, experience and analogy he is able to draw some conclusions about the kind of world in which he lives and about his own nature. Although Anaxagoras' thesis left many problems, it was perhaps one of the most brilliant solutions in Presocratic philosophy.
Reesor, Margaret, "The Problem of Anaxagoras" (1960). The Society for Ancient Greek Philosophy Newsletter. 62.