One part of a picture ought to be like the first part of a tune, that you guess what follows, and that makes the second part of the tune, and so I'm done..

letter to his friend William Jackson of Exeter, from Bath, Feb. 1768; as cited in Thomas Gainsborough, by William T, Whitley; New York, Charles Scribner's Sons – London, Smith, Elder & Co, Sept. 1915, p. 383 (Appendix A - Letter V)