In his On the study of character including an estimate of phrenology, Alexander Bain aims to construct a differential psychology on the foundation of his general psychology, which attempts to ascertain the universal laws of thought. This Study, which is by and large a failure, shows how Bain, in his analysis of individual differences, was dependent on phrenology. Furthermore, the importance which Bain gives to the biological and psychological determinants of character separates him by a considerable distance from John Stuart Mill over the status of ethology. Such a consequence is paradoxical : with this Study of character, Bain certainly intended to fulfill Mill’s project of creating a science of human nature.