Anaxagoras was the man in whom philosophy first truly entered the great city. He moved to Athens — in the age of its flowering — and became a close friend of Pericles, assisting him in political affairs. And there, amid the noise of the democratic polis, he continued to ponder the very question over which all early Greek thought had struggled: being is whole and one, but how does life unfold within it, how does this ceaseless motion and generation of things proceed?
His answer differed from that of his predecessors. Whereas Empedocles reduced everything to four elements, Anaxagoras spoke of a multitude of qualitatively distinct things, infinitely divisible besides. However finely we divide a particle, it can always be divided further — division has no limit. These smallest particles he called homoeomeries, the seeds of things. At some level they no longer have either mass or volume — only pure essence remains.
He was led to this thought by a simple yet profound question: why does a human being grow? A newborn child is small, and then it grows — nourished first by its mother's milk, then by bread. But bread, after all, is made of wheat, not of hair, nails, or flesh — so where does the growing body come from? It follows, Anaxagoras concluded, that the seeds of all things are already contained within each thing. Wheat, too, grows out of the earth in this way: we bury our dead in the earth, they decompose and return to it, and from that same earth wheat rises again — a cycle of seeds in which everything contains everything.
Hence his famous principle: everything in everything. In every thing, in each of us, there is present, as it were, an entire world, all the homoeomeries at once. This was a bold idea of pure essences — a level of being at which corporeality no longer exists, but only essences remain, out of which corporeal things are merely composed.
But who, then, orders these seeds, gathering them into well-formed bodies and things? Here Anaxagoras introduces a principle destined for a great future — Mind, Nous. This is the supreme, divine Mind, separate from all things and mixed with nothing; it is the origin of all things and governs all things, transforming pure essences into bodies. It is true, however, that it was precisely in this transformation of essences into bodies that Democritus would later notice a vulnerability, and take it as the point from which to build his own teaching.
The significance of Anaxagoras is twofold. On the one hand, purely speculatively, without any instruments or microscopes, he managed to anticipate what science would arrive at only many centuries later: that at the level of the smallest particles, familiar corporeal matter, as it were, disappears, dissolving into pure essences. On the other hand, he was the first to place clearly, above the whole universe, an ordering intelligence, Mind, and thereby threw a bridge toward the future idea of God as pure mind and consciousness. Alongside Parmenides, who proved the wholeness of being, and Empedocles, who sought how the many is born from the one, Anaxagoras remains one of those who prepared the ground for all of mature philosophy.