Anaxagoras's theory of mixture represents a totally new move in the plurality question. Whereas the other Presocratics (Parmenides and his followers excluded) asked how a plurality could arise out of a unity, Anaxagoras bypasses the whole issue by claiming that there is a full plurality to begin with. There never really was a unity at all, since in every piece of matter, no matter how small, pieces of every other homeomeric substance is mixed in (to make this view possible, incidentally, Anaxagoras needs to hold to his principle of infinite divisibility, for which he is indebted to Zeno of Elea).
Given that all things are in all things, it might seem that the process of identifying objects should get rather confusing, but in fact Anaxagoras has a neat solution to this worry. We identify things by the proportional amount of homeomeric substance in the mixture. Just like on Empedocles' view, objects were identified by the ratio of the four elements in their recipe, here too objects are identified by the dominant homeomeric substances in their recipe.
Like his Milesian forebears, Anaxagoras uses his metaphysical theory as the basis of a cosmogony (or theory of the origins of the world). He paints a picture in which originally what existed was a primordial mixture containing all things. This original mixture was then set into motion, and the different parts were separated off. These then recombined with each other to produce the world as we perceive it.
What Anaxagoras means by claiming that "all things" were in this original mixture is unclear. He probably means that all homeomeric substances were originally in this mixture, and that they were what then separated off when the motion began. This seems like the most plausible interpretation, especially given the fact that the homeomeric substances, as Parmenidean Reals, could not have been generated. Some commentators, however, have read this passage differently. Some believe that Anaxagoras meant to claim that all possible objects of the world were in this mixture, but there seems to be no reason for him to have made this strong claim. Others believe that it was only the opposites that were in this mixture, but this would then make it seem as if the homeomeric substances were generated.
Because of the Eleatic attack on change, Anaxagoras could not make a weak appeal to eternal motion when explaining how his original mixture got moving. To what, then, does he appeal? The confused mass gets started in the process of differentiation by the one thing not mixed in with anything else: mind or nous.
Anaxagoras's mind is somewhat akin to Heraclitus' logos, insofar as it is the rationality that controls nature. Mind is infinite and self-ruled, and like the logos, it is very much a part of the physical world. It also, however, takes on the role of Empedocles' love and strife as the motive force in the world.