Anaxagoras draws on the metaphysics of Parmenides in his theory of reality. He maintains the idea that what-is cannot not be, as well as the idea that all things are present in the whole. Hence he argues that all things have existed and continue to exist together, and that visible reality is merely the combination of these ingredients. Like Empedocles, he envisions a dissociating force, though everything has a share in everything else. He also employs the argument used by Parmenides and Empedocles which reasons that nothing can be added to the whole because the whole already contains everything which is, and nothing comes from what is not.
However, Anaxagoras provides us with a novel contribution to this basic metaphysical theory. Aristotle writes concerning Anaxagoras, "When someone said that Nous is present - in nature just as it is in animals - as the cause of the kosmos and of all its order, he appeared as a sober man among the random chatterers who preceded him" (Curd, 107). Anaxagoras thinks that Mind is fundamental aspect of reality. He argues, "The other things have a share of everything, but Nous is unlimited and self-ruling and has been mixed with no thing, but is alone itself by itself. For if it were not by itself, but had been mixed with anything else, then it would partake of all things" (Curd, 104). Because everything shares in everything else, if Mind shared in something, then it would share in everything else as well. However, Simplicius reports that "In everything there is a share of everything except Nous (Mind), but there are some things in which Nous, too, is present" (Curd, 104). This seems to lead to a contradiction, but it is apparent that nous is a thing which exists in some creatures.
Unfortunately, I can find in Anaxagoras no resources for resolving such a contradiction. Perhaps later philosophers will find a solution, but Anaxagoras himself does not seem to explicitly resolve it. Or, it may be the case that our sources have not accurately recorded his reasoning. Whatever the case may be, Anaxagoras argument for Nous as something present in reality provides a new and interesting dimension for metaphysical inquiry. Other philosophers presented seemingly intelligent beings such as Love and Hate in their cosmologies, but Anaxagoras is the first of the Presocratics that we have seen to present Mind itself as a feature of reality.