Look at Jerusalem, Plates 12 and 13:
"Fourfold the Sons of Los in their divisions: and fourfold,In simple terms the Fall of Albion from Eden involved his division into four zoas (Jung had a similar construction which he called the four functions of the psyche. Individuation would involve four perfectly balanced functions.) In Western thought the only such man would be Jesus. All the rest of us are one sided in some way: reason oriented (urizenic), feeling oriented (luvan), sensation oriented (tharman (this really doesn't seem to work quite right?), and imagination or intuition (urthonian) (down here in the world Urthona is represented by Los). If this is confusing, press on perhaps for more confusion (but remember that confusion is the first step in understanding).
The great City of Golgonooza: fourfold toward the north
And toward the south fourfold, & fourfold toward the east & west
Each within other toward the four points: that toward
Eden, and that toward the World of Generation,
And that toward Beulah, and that toward Ulro:
Ulro is the space of the terrible starry wheels of Albions sons:
But that toward Eden is walled up, till time of renovation:
Yet it is perfect in its building, ornaments & perfection.
And the Four Points are thus beheld in Great Eternity
West, the Circumference: South, the Zenith: North,
The Nadir: East, the Center, unapproachable for ever.
These are the four Faces towards the Four Worlds of Humanity
In every Man. Ezekiel saw them by Chebars flood.
And the Eyes are the South, and the Nostrils are the East.
And the Tongue is the West, and the Ear is the North.
And the North Gate of Golgonooza toward Generation;
Has four sculpturd Bulls terrible before the Gate of iron.
And iron, the Bulls: and that which looks toward Ulro,
Clay bak'd & enamel'd, eternal glowing as four furnaces:
Turning upon the Wheels of Albions sons with enormous power.
And that toward Beulah four, gold, silver, brass, & iron:
And that toward Eden, four, form'd of gold, silver, brass, &
The South, a golden Gate, has four Lions terrible, living!
That toward Generation, four, of iron carv'd wondrous:
That toward Ulro, four, clay bak'd, laborious workmanship
That toward Eden, four; immortal gold, silver, brass & iron.
The Western Gate fourfold, is closd: having four Cherubim
Its guards, living, the work of elemental hands, laborious task!
Like Men, hermaphroditic, each winged with eight wings
That towards Generation, iron; that toward Beulah, stone;
That toward Ulro, clay: that toward Eden, metals.
But all clos'd up till the last day, when the graves shall yield
The Eastern Gate, fourfold: terrible & deadly its ornaments:
Taking their forms from the Wheels of Albions sons; as cogs
Are formd in a wheel, to fit the cogs of the adverse wheel.
That toward Eden, eternal ice, frozen in seven folds
Of forms of death: and that toward Beulah, stone:
The seven diseases of the earth are carved terrible.
And that toward Ulro, forms of war: seven enormities:
And that toward Generation, seven generative forms.
And every part of the City is fourfold; & every inhabitant,
There's more light on that confusion in this description of the four men found in A Descriptive Catalog (in Erdman 543):
"The Strong man represents the human sublime. The Beautiful man represents the human pathetic, which was in the wars of Eden divided into male and female. The Ugly man represents the human reason. They were originally one man, who was fourfold; he was self-divided, and his real humanity slain on the stems of generation, and the form of the fourth was like the Son of God."
(That last line vividly echoes the fourth man found strolling in the furnace with Shadrach, Meshach, and Abednego (at Daniel 3:25)
(In regard to the Strong, Beautiful and Ugly men look for more detail at Ancient Britons.)
In a similar vein, in a letter to Butts, Blake touched on the four levels of consciousness; here's the most salient fragment:
"Now I a fourfold vision see And a fourfold vision is given to me
Tis fourfold in my supreme delight And three fold in soft Beulahs night And twofold Always. May God us keep From Single vision & Newtons sleep"
(Letter 23; Erdman 722)
So what might single vision be? A logical positivist might have single vision; he thinks that there is no meaning except objects that can be weighed and measured.
But can love be weighed and measured? "Meaningless" says the man with single vision. Blake said:
"Can Wisdom be put in a silver rod?
Or Love in a golden bowl?"
(From Thel's Motto on page 3 of Erdman)