The author offers a systematic introduction to central philosophical problems, opening with an account of doubt, the limits of knowledge, and the corrective relation between philosophy and science. He examines perception, learning, language, memory, and inference; analyzes physical theory, causation, and the relation between physics and perceptual experience; and turns to introspective topics such as imagery, imagination, consciousness, emotion, desire, will, and ethics. The work concludes by surveying major historical doctrines and addressing truth, the validity of inference, the relation of mind and matter, and humanity’s place in the universe.