1. Donald Palmer, Does the Center Hold? (Mountain View: May-field, 1991), pp. 18–23.
2. Frattaroli, pp. 73–76.
3. Donald Palmer, Looking at Philosophy (Mountain View: May-field, 1988), pp. 4–32, 69.
4. Diane Collinson, Fifty Major Philosophers (London: Croom Helm, 1987), pp. 17–18.
5. Anthony Flew, A Dictionary of Philosophy (New York: St. Martin’s Press, 1979), pp. 88, 203.