From Wikipedia (15 mar 2010)
Negative capability is a theory of the poet John Keats describing the capacity for accepting uncertainty and the unresolved.
Keats’ theory of “negative capability” was expressed in his letter to his brother dated Sunday, 21 December 1817. He says 
I had not a dispute but a disquisition with Dilke, on various subjects; several things dovetailed in my mind, & at once it struck me, what quality went to form a Man of Achievement especially in literature & which Shakespeare possessed so enormously – I mean Negative Capability, that is when man is capable of being in uncertainties, Mysteries, doubts without any irritable reaching after fact & reason.
Keats believed that great people (especially poets) have the ability to accept that not everything can be resolved. Keats, as a Romantic, believed that the truths found in the imagination access holy authority. Such authority cannot otherwise be understood, and thus he writes of “uncertainties.” This “being in uncertaint[y]” is a place between the mundane, ready reality and the multiple potentials of a more fully understood existence. It relates to his metaphor of the Mansion of Many Apartments.
It could be argued that Keats explored this idea in several of his poems:
• La Belle Dame sans Merci: A Ballad (1819)
• Ode to a Nightingale (1819)
• The Fall of Hyperion: A Dream (1819)
• Ode on a Grecian Urn (1819)
Negative capability is a state of intentional open-mindedness paralleled in the literary and philosophic stances of other writers. In the 1930s, the American philosopher John Dewey cited Keatsian negative capability as having influenced his own philosophical pragmatism, and said of Keats’ letter that it “contains more of the psychology of productive thought than many treatises.”   Nathan Scott, in his book Negative capability; studies in the new literature and the religious situation , notes that negative capability has been compared to Heidegger’s concept of Gelassenheit, “the spirit of disponibilité before What-Is which permits us simply to let things be in whatever may be their uncertainty and their mystery.” Walter Jackson Bate, Keats’s biographer, explored the approach in detail in his 1968 work Negative Capability: The Intuitive Approach in Keats.
Author Philip Pullman excerpts from Keats’s letter and prominently incorporates the concept in his fantasy novel The Subtle Knife.
1. Romanticism: an anthology, By Duncan Wu, Duncan Wu Edition: 3, illustrated Published by Blackwell, 2005 p.1351
2. Dewey, John. Art as Experience. New York: Penguin Perigree (2005):33-4.
3. Kestenbaum, Victor. The Grace and the Severity of the Ideal: John Dewey and the Transcendent. Chicago: University of Chicago Press (2002): 225.
4. Scott. Negative capability; studies in the new literature and the religious situation. Yale University Press (New Haven), 1969