1. P. Unger, ‘A Defense of Skepticism’, Philosophical Review
80 (1971), 216
2. See P. Unger, ‘Two Types of Skepticism’, Philosophical Studies
25 (1974), 77–96
3. C.I. Lewis, ‘The Bases of Empirical Knowledge’, in Chisholm and Swartz (eds.), op. cit., p. 137
4. See Lewis, An Analysis of Knowledge and Valuation, pp. 303–306
5. N. Goodman, ‘Sense and Certainty’, Philosophical Review
61 (1952). Reprinted in Chisholm and Swartz (eds.), op.cit., p. 361