In his later philosophy, Russell subscribed to a kind of neutral monism , maintaining that the distinctions between the material and mental worlds, in the final analysis, were arbitrary, and that both can be reduced to a neutral property—a view similar to one held by the American philosopher/psychologist, William James , and one that was first formulated by Baruch Spinoza , whom Russell greatly admired.  Instead of James' "pure experience," however, Russell characterised the stuff of our initial states of perception as "events," a stance which is curiously akin to his old teacher Whitehead's process philosophy .
In 1972–1973 Ayer gave the Gifford Lectures at University of St Andrews , later published as The Central Questions of Philosophy . In the preface to the book, he defends his selection to hold the lectureship on the basis that Lord Gifford wished to promote '"Natural Theology", in the widest sense of that term', and that non-believers are allowed to give the lectures if they are "able reverent men, true thinkers, sincere lovers of and earnest inquirers after truth".  He still believed in the viewpoint he shared with the logical positivists: that large parts of what was traditionally called "philosophy"– including the whole of metaphysics , theology and aesthetics – were not matters that could be judged as being true or false and that it was thus meaningless to discuss them.