20th-century philosophy saw the development of a number of new philosophical schools—including logical positivism, analytic philosophy, phenomenology, existentialism, and poststructuralism. In terms of the eras of philosophy, it is usually labelled as contemporary philosophy (succeeding modern philosophy, which runs roughly from the time of René Descartes until the late 19th to early 20th centuries). The publication of Edmund Husserl's Logical Investigations (1900–1) and Bertrand Russell's The Principles of Mathematics (1903) is considered to mark the beginning of 20th-century philosophy.