Ward's lecture series (Naturalism and Agnosticism) seeks to defend an adequate basis for theistic inquiry in light of certain assumptions made by science that would preclude such an inquiry's possibility. Naturalism has a tendency to favour materialism. Where naturalism takes agnosticism for its ally (something it must do if its doctrines are not to remain dogma) and is, thereby, forced to choose between spiritualism and materialism, it opts for the materialist terminology (albeit for practical purposes in the progression of scientific enquiry).

Arend’s Gifford Lectures, ‘Critique of Heaven and Earth’, delivered in Aberdeen in 1970 and 1972, were published in two volumes: Critique of Heaven (1972) and Critique of Earth (1974). The series sets out to address something of a revolution in the domain of natural theology through an investigation of the works of Karl Marx.