Letters on Poetry and Art
SABCL - Volume 27
Part 2. On His Own and Others’ Poetry
Section 1. On His Poetry and Poetic Method
Comments on Specific Lines and Passages of the Poem 
I notice that you have changed “twixt” to “between” when substituting “link” for “step” in the line, “Air was a vibrant link between earth and heaven.” [p. 4] Is it merely because several lines earlier “twixt” has been used?
No, it is because “link twixt”, two heavy syllables (heavy because ending in two consonants) with the same vowel, makes an awkward combination which can only be saved by good management of the whole line — but here the line was not written to suit such a combination, so it won’t do.
28 October 1936