What is photography? Is it a source of knowledge or an art? Many have said the former because it records the world automatically, others the latter because it expresses human subjectivity. Can photography be both or must we choose? In On Photography: A Philosophical Inquiry, Diarmuid Costello examines these fascinating questions and more, drawing on images by Alfred Stieglitz, Berenice Abbott, Paul Strand, Lee Friedlander, James Welling,...