As quoted by Howard, op. cit., vol. ii, p. 29.
Ellen Key similarly (Ueber Liebe und Ehe, p. 343) remarks that to talk of "the duty of life-long fidelity" is much the same as to talk of "the duty of life-long health." A man may promise, she adds, to do his best to preserve his life, or his love; he cannot unconditionally undertake to preserve them.
Hobhouse, op. cit., vol. 1, pp. 159, 237-9; cf. P. and V. Margueritte, Quelques Idées.