Commentary on Blake's six illustrations to Milton's Il Penseroso is found in Bette Charlene Werner's book Blake's vision of the poetry of Milton: illustrations to six poems. Blake 'invented', (he signed images WBlake inv), the third illustration The Spirit of Plato as a means of presenting a number of Plato's ideas as Milton contemplated them.
"Or let my lamp, at midnight hour,
Be seen in some high lonely tower,
Where I may oft outwatch the Bear,
With thrice great Hermes, or unsphere
The spirit of Plato, to unfold
What worlds or what vast regions hold
The immortal mind that hath forsook
Her mansion in this fleshly nook;
And of those demons that are found
In fire, air, flood, or underground," (lines 85-95)
In the picture we see how Plato divided the soul between the three worlds of Venus, Jupiter, Mars - senses, reason and energy. The Great Bear is the constellation around which the constellations revolve; it never sets - symbolizing an ever circling round.
Blake added a few lines of descriptive material to each of his illustrations to Il Penseroso. Blake's description: "The Spirit of Plato unfolds his Worlds to Milton in Contemplation. The three destinies sit on the Circles of Plato's Heavens weaving their Thread of Mortal Life; these Heavens are Venus Jupiter and Mars. Hermes flies before as attending on the Heaven of Jupiter, the Great Bear is seen in the Sky beneath Hermes & The Spirits of Fire, Air, Water & Earth Surround Milton's Chair."
In this the third illustration to Il Penseroso illustrating lines 85-95 of Milton's poem, Blake goes to pains to include the import of the lines of the poem but adds details to indicate the ideas of Plato to which he objected.
Damon enumerates the points at which Plato's thought differed from Blake's:
"Thus it is that although Plato banished poets from his Republic, made God a geometrician, preached morality, was a fatalist when he accepted the Three Fates, debased love to homosexuality, admitted war to his ideal state, and considered Art an imitation of Nature (hence second rate), Blake was indebted to him." Blake knew that there was much to be admired in Plato's thought although he said that "What Jesus came to remove was the Heathen or Platonic Philosophy, which blinds the eye to Imagination, The real Man." (E 664 ). Blake portrays the Greek learned and wise among the saved in the Last Judgment.
The prominence in the illustration of Hermes perhaps in his role of as the guide for souls in the underworld, may be Blake's assertion that both Plato and Milton are still in need of guidance in matters of the soul. None of the Platonic images contemplated by Milton seems to show the positive outcome for Man's plight for which Blake is working.
Blake's ambivalence to Plato and Greek thought can be seen in these 2 short passages:
Songs and Ballads,(E 479)
"Twas the Greeks love of war
Turnd Love into a Boy
And Woman into a Statue of Stone
And away fled every joy"
Letter to Trusler, (E 702)
"The wisest of the Ancients considerd what is not
too Explicit as the fittest for Instruction because it rouzes the
faculties to act. I name Moses Solomon Esop Homer Plato"