‘Empirical Propositions and Hypothetical Statements’, Mind 59 (1950), 289–312

• repr. in Robert J. Schwartz (ed.), Perceiving, Sensing, and Knowing (New York, 1965: Doubleday), Mark J. Smith (ed.), Philosophy and Methodology of the Social Sciences, vol. 1, Canons and Custodians: Scientific Enquiry in the 20th Century (London, 2005: Sage), 71–94
• Concepts and Categories