 An early influence on Berlin was a waning British Idealism, as expounded by T. H. Green, Bernard Bosanquet and F. H. Bradley. While an undergraduate, Berlin was converted to the Realism of G. E. Moore and John Cook Wilson. By the time he began teaching philosophy he had joined a new generation of rebellious empiricists, some of whom (most notably A. J. Ayer) embraced the logical positivist doctrines of the Vienna Circle and Wittgenstein’s earlier writings. Although Berlin was always sceptical towards logical positivism, its suspicion of metaphysical claims and its preoccupation with the nature and authority of knowledge strongly influenced his early philosophical enquiries. These, combined with his historical bent, led him back to the study of earlier British empiricists, particularly Berkeley and Hume, on whom he lectured in the 1930s and late 1940s, and about whom he contemplated writing books (which never materialised).