Wallace Stevens’ ‘An Old Man Asleep’ implies the between between ‘the self and the earth’ and ends with one of Stevens’ rapturous though apophatic images: ‘The river motion, the drowsy motion of the river R.’ The between space is one of passage between extremes, extremes like ‘the river R.’
You might call the between the poetics of myth, of story. Poets like Stevens, knowing that ‘these extremes are recessed in the domestication of everyday life’ (William Desmond, The Gift of Beauty and the Passion of Bejng, p. 253), make poems by telling stories about ‘diverse extremes: birth and death, nothing and infinity, abysses if abjectness and superlatives of heights, inferiorities of secret intensity and exteriorities of vast extension’ (ibid.).
The between is the grammar of human consciousness.