Spencer, H. (1891). The Principles of Ethics (2nd thousand.). Williams and Norgate.
Citazione stile Chigago Style (17a edizione)Spencer, Herbert. The Principles of Ethics. 2nd thousand. London ; Edinburgh: Williams and Norgate, 1891.
Citatione MLA (8a ed.)Spencer, Herbert. The Principles of Ethics. 2nd thousand. Williams and Norgate, 1891.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.