Sidgwick's History of Ethics (1902), pp. 198 sq.
Alfred Sidgwick's logical writings, especially his Distinction (1892) and The Use of Words in Argument (1901), represent an independent development.
Sidgwick's Methods of Ethics (6th ed., 1901), p. 384; A.
Parish, Hallucinations and Illusions and Zur Kritik des telepathischen Beweismaterials, and Mrs Sidgwick's refutation in Proc. S.P.R.
Even before the appearance of Sidgwick's book utilitarianism had entered upon its third or evolutional phase, in which principles borrowed from biological science make their entrance into moral philosophy.