In this paragraph of Stoner by John Williams:
Walker nodded and began swiftly to speak. "I intend to trace Shelley's first rejection of Godwinian necessitarianism for a more or less Platonic ideal, in the 'Hymn to Intellectual Beauty,' through the mature use of that ideal, in Prometheus Unbound, as a comprehensive synthesis of his earlier atheism, radicalism, Christianity, and scientific necessitarianism, and ultimately to account for the decay of the ideal in such a late work as Hellas.
What does "rejection of Godwinian necessitarianism for a more or less Platonic ideal" mean?