Keats' "Negative Capability" has become a lit-crit commonplace, so that scholars and readers forget the richness of its significations. To balance psycho-affective polarities without "irritably grasping after reason" (or principles, in the Kantian sense, which specifically suggests deductive reasoning and its sobriety, against the aesthetic) is one cognitive level Negative Capability accounts for; but the other question (which the Odes answer) is how polarities might be expressed in text in a negatively capable fashion. To achieve this end in the most spectacular possible fashion, Keats has recourse to dialects of sense/sensibility, initiated from a subjective stance of acknowledgement of the darkness of physical extinction, while maintaining affective vivacity in relation to his own psycho-affective processes- all the data being processed finds worthwhile and illustrative objective correlatives in what Keats opens textually. Keats' objective correlatives in the Odes- his nightingale, Grecian Urn, autumn, melancholy, and the rest- have a way of jolting his textual gambits up from sensibility to understanding and then (importantly, by induction rather than deduction) distilled/principled reason, not initially grasped for but floated up to gracefully and artfully.
The time/space coordinates projected by Keats onto his Odal objects create dynamic tensions which torque and transform depending on any given reader's subjectivity- the succession of vignettes in "Nightingale," in particular, create a warped sense of temporal textual succession, in which a succession of disappearances is enacted (the poet, the nightingale, the song, the state of consciousness and entire sensibility which illuminated the succession as a landscape, a forest scene), so that conventional space/time coordinates are replaced as the eruption of time zones is followed by dissolution of the same; and the conceptions which arise from this enactment, animated by the Odal objective correlatives, have to do with an essential mutability inhering in the congealed formal matter of Keats' subjectivity, which it is the unique province of major high art consonant poetry to reveal. This breach in time/space coordinates is explosive, spectacular, compulsively demonstrative; in short, Romantic; and that, the demonstration of psycho-affective mutability potentialities, is what Romanticism at its best brings to the philosophical table, against the conceptually grounded stability of the higher echelons of (philosophic/scientific) prose, their vistas onto human collectives.
The lyric poet, Adorno writes, is self-posited against society; and defines himself in relation to the entire human continuum of types which he is not; isolated by his (or her) capacity for mutability (on psycho-affective levels) and cognitive boundary-dissolution (into, presumably, transcendental realms once conventional frameworks are eliminated), but also ossified into a kind of stunted adolescence by his (or her) inability to view things plainly, and discern profound truth from illusion. That's why, though Keats' textual bravery exceeds Wordsworth's, and his confrontations with mortality are affecting, his appeal still lies in this inducement, often via prosody, of states of intoxication. If textual truth accords with textual beauty (to follow Grecian Urn through), Keats must fare relatively poorly next to philosophic prose, whose concerns and efforts wear more comfortably over long periods of time. Through this textual strainer, Keats' apogee of intoxication is assimilated and the central Romantic fallacy pierced through- that the dissolution of boundaries, psychic and otherwise, is commensurate with a kind of enlightenment, aesthetic or otherwise.