 In some of his later works in the field, particularly his “Epistemology Without a Knowing Subject” (1967, republished in Objective Knowledge [1972]) and in his lecture “Three Worlds” in the Tanner Lectures on Human Values delivered in 1978 (published 1980), Popper develops the notion of objectivity further in a novel but controversial way by seeking to free it completely from all psychological constraints. What is central to epistemology, he reaffirms, is the concept of objectivity, which he seeks to show requires neither the notions of subjective mental states nor even that of a subject “possessing” knowledge: knowledge in its full objective sense, he argues, is knowledge “without a knowing subject”.