Plotinus, the founder of Neoplatonism, was the last profoundly creative thinker of the ancient pagan world. He was an original and penetrating interpreter of Plato, and his importance in the history of ideas rests on his formulation of a new version of Platonism that made it a credible and satisfying option in a world that had changed considerably since Plato's own day. In this version, to be sure, much of what Plato himself considered important virtually disappears. But while losing something of the range of Plato's thought, Plotinus focuses and enriches an aspect of that thought that has always been its most inspirational feature, namely, the Athenian philosopher's defense of his confidence in the superior value and reality of another world, a "higher" realm in which everything that is deficient, ephemeral, and incomplete in the "lower" realm of sense is overcome.

The key interpretive move that enabled Plotinus...