 Prior to the twentieth century, a substantial amount of philosophical reflection on matters of religious significance (but not all) has been realist. That is, it has often been held that religious beliefs are true or false. Xenophanes and other pre-Socratic thinkers, Socrates, Plato, Aristotle, the Epicureans, the Stoics, Philo, Plotinus differed on their beliefs (or speculation) about the divine, and they and their contemporaries differed about skepticism, but they held (for example) that there either was a divine reality or not. Medieval and modern Jewish, Christian, and Islamic philosophers differed in terms of their assessment of faith and reason. They also faced important philosophical questions about the authority of revelation claims in the Hebrew Bible, the Christian Bible, and the Qur’an. In Asian philosophy of religion, some religions do not include revelation claims, as in Buddhism and Confucianism, but Hindu tradition confronted philosophers with assessing the Vedas and Upanishads. But for the most part, philosophers in the West and East thought there were truths about whether there is a God, the soul, an afterlife, that which is sacred (whether these are known or understood by any human being or not). Realism of some kind is so pervasive that the great historian of philosophy Richard Popkin (1923–2005) once defined philosophy as “the attempt the give an account of what is true and what is important” (Popkin 1999: 1). Important philosophers in the West such as Immanuel Kant (1724–1804) and Friedrich Nietzsche (1844–1900), among others, challenged classical realist views of truth and metaphysics (ontology or the theory of what is), but the twentieth century saw two, especially powerful movements that challenged realism: logical positivism and philosophy of religion inspired by Wittgenstein.