Keats writes to Fanny Brawne, 24(?) February 1820:

Do you hear the thrush singing over the field? I think it is a sign of mild weather so much the better for me. Like all Sinners now I am ill I philosophise aye out of my attachment to every thing, Trees, flowers, Thrushes Spring, Summer, Claret &c &c aye every thing but you my Sister would be glad of my company a little longer.

(Letters, ed. Rollins, II, 265)

A few days earlier he had written to Fanny 'I must make myself as good a Philosopher as possible.' By this Keats seems not to mean he must study Philosophy, but that he must be stoical, resolute in the face of his illness. But that will involve turning his mind from that which most attaches him to life - the phrase interrupts a sentence that begins 'Even if I was well -'. He is stopping himself from thinking of the thwarted life with Fanny, just as in that first quotation, he claims to be emptying his thoughts of all sensuous things, particulars - trees, flowers, summer, thrushes, claret - everything but her. He is abstracting himself from these things.

Sometimes poetry itself seems to be one of these things. In a letter to Sarah Jeffrey in June 1819, he writes:

I have been very idle lately, very averse to writing; both from the overpowering idea of our dead ...