It's Keats talking about Shakespeare in a letter:
http://classweb.gmu.edu/rnanian/Keats-NegativeCapability.html
Brown and Dilke walked with me and back from the Christmas pantomime. I had not a dispute but a disquisition, with Dilke on various subjects; several things dove-tailed in my mind, and at once it struck me what quality went to form a Man of Achievement, especially in Literature, and which Shakespeare possessed so enormously I mean Negative Capability, that is, when a man is capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason Coleridge, for instance, would let go by a fine isolated verisimilitude caught from the Penetralium of mystery, from being incapable of remaining content with half-knowledge. This pursued through volumes would perhaps take us no further than this, that with a great poet the sense of Beauty overcomes every other consideration, or rather obliterates all consideration.
^^^^^^^ CB: I think the Brown Keats refers to is me (smile)
http://en.wikipedia.org/wiki/Charles_Armitage_Brown
He published many articles in English periodicals, the best-known being "Shakespeare's Fools" in 1823.
* Shakespeare's Autobiographical Poems, by Charles Armitage Brown, London: J. Bohn, 1838
The Life of John Keats by Charles Armitage Brown Brown was Keats's closest friend. His Life of John Keats, revised and completed twenty years after the poet's death, offers unique insight into Keats's life.
http://englishhistory.net/keats/brownkeats.html
1816
CHARACTER OF CHARLES BROWN
by John Keats
I.
He is to weet a melancholy carle:
Thin in the waist, with bushy head of hair
As hath the seeded thistle when in parle
It holds the Zephyr, ere it sendeth fair
Its light balloons into the summer air;
Therto his beard had not begun to bloom,
No brush had touch'd his chin or razor sheer;
No care had touch'd his cheek with mortal doom,
But new he was and bright as scarf from Persian loom.
II.
Ne cared he for wine, or half-and-half;
Ne cared he for fish or flesh or fowl,
And sauces held he worthless as the chaff,
He 'sdeigned the swine-head at the wassail-bowl;
Ne with lewd ribbalds sat he cheek by jowl,
Ne with sly Lemans in the scorner's chair;
But after water-brooks this Pilgrim's soul
Panted, and all his food was woodland air
Though he would oft-times feast on gilliflowers rare.
III.
The slang of cities in no wise he knew,
Tipping the wink to him was heathen Greek;
He sipp'd no olden Tom or ruin blue,
Or nantz or cherry-brandy drank full meek
By many a damsel hoarse and rouge of cheek;
Nor did he know each aged watchman's beat,
Nor in obscured purlieus would he seek
For curled Jewesses with ankles neat,
Who as they walk abroad make tinkling with their feet.
THE END .