 He is co-author of "The Animal Rights Debate" (Rowman and Littlefield, 2001), a point-counterpoint volume with Tom Regan; he is also the author of "Democracy" (Macmillan, 1972); the author of "Four Systems" (Random House, 1982); the editor of "Communism, Fascism, and Democracy" (McGraw Hill, 1997); the co-author (with J. Sterba) of "Affirmative Action and Racial Preference" (Oxford, 2003), co-author (with I. M. Copi) of "Introduction to Logic, 13th edition" (Prentice-Hall, 2008), and author of "A Conflict of Principles