David Kelley, The Evidence of the Senses: A Realist Theory of Perception (Baton Rouge: Louisiana State University Press, 1986).
Abstraction and concepts
Allan Gotthelf, “Ayn Rand on Concepts: A New Approach to Abstraction, Essences, and Kinds”
David Kelley, “Rand Versus Hayek on Abstraction,” Reason Papers vol. 33 (Fall 2011), pp. 12-30.
David Kelley, “A Theory of Abstraction,” Cognition and Brain Theory vol. 7:3-4 (1984), pp. 329-57.
Concepts, units, measurement-omission
Steven Yates, “Ayn Rand on Units, Essences, and the Intrinsic,” Reason Papers vol. 20 (Fall 1995), pp. 35-54.
Epistemic justification and related issues
David Kelley, “Evidence and Justification,” Reason Papers vol. 16 (Fall 1991), pp. 165-79.