In 1824, Lady Mary Shepherd (1777–1847) published An Essay upon the Relation of Cause and Effect. This book was sharply critical of Hume's account of causation, and included some additional criticisms of the views of two early nineteenth-century proponents of Hume’s account. In the Preface to her next book, the 1827 Essays on the Perception of an External Universe, Shepherd wrote that she had wished to include such an essay as an appendix to the 1824 book, but that, 'finding the notions which suggested themselves would exceed the limit of that work’, she had decided to address these ideas in a second book. In addition to the long essay on the nature of the external world and how we perceive it, the 1827 book contains fourteen short essays on related topics. Since Shepherd herself conceived of the 1824 and 1827 works as linked, it is appropriate that they now be published together.