Dayadhvam: I have heard the key
Turn in the door once and turn once only
We think of the key, each in his prison
Thinking of the key, each confirms a prison
411. Cf. Inferno
, XXXIII, 46:
“ed io sentii chiavar l’uscio di sotto
Also F. H. Bradley, Appearance and Reality, p. 346:
“My external sensations are no less private to myself than are my thoughts or my feelings. In either case my experience falls within my own circle, a circle closed on the outside; and, with all its elements alike, every sphere is opaque to the others which surround it... In brief, regarded as an existence which appears in a soul, the whole world for each is peculiar and private to that soul.”
The first part of Eliot's note draws from Canto 33, lines 46-47, of Dante's Inferno:
“Below I heard them nailing up the door
Of the horrible tower
The speaker is Count Ugolino, an Italian nobleman. A rival captured Ugolino, along with his sons and grandsons, and imprisoned them in a tower. The tower was locked and the count and his family were left to starve. For a brief overview of The Divine Comedy, see the note to the dedication.
The second part of the note is a quote from the British philosopher F. H. Bradley. Bradley's Appearance and Reality argues that each person's experience of the world is unique and that communication between people is therefore fundamentally ambiguous. Bradley was the subject of Eliot's abandoned dissertation work.