Despite its misleading name (it doesn't talk much about metaphysics, and it's pretty short for a treatise), this early work by Voltaire questions everything including God, the immortality of the soul, free will, theology, and objective morality, the nature of man, and social norms. This is a new English translation. Table of Contents from the book: Introduction: Doubts on Man. 1: On the Different Species of Men. 2: Whether There Is a God. 3: That All Ideas Come via the Senses. 4: That There Really Are External Objects. 5: Whether Man Has a Soul, and What This Might Be. 6: Whether What Is Called the Soul Is Immortal. 7: Whether Man Is Free. 8: On Man Considered as a Sociable Being. 9: On Virtue and Vice.