Barnstone, Willis, Six Masters of the Spanish Sonnet, Southern Illinois University Press, 1993, pp. 104, 107.

Machado, Antonio, Selected Poems, translated and with an introduction by Alan S. Trueblood, Harvard University Press, 1982, pp. 262-65.

Trueblood, Alan S., “Antonio Machado and the Lyric of Ideas,” in Letter and Spirit in Hispanic Writers: Renaissance to Civil War, Tamesis Books Limited, 1986, p. 255.