In philosophy, panpsychism is the view that consciousness, mind or soul (psyche) is a universal and primordial feature of all things. Panpsychists see themselves as minds in a world of mind. Panpsychism is one of the oldest philosophical theories, and has been ascribed to philosophers like Thales, Plato, Spinoza, Leibniz and William James. Panpsychism can also be seen in ancient philosophies such as Stoicism, Vedanta and Mahayana Buddhism. During the 19th century, panpsychism was the default theory in philosophy of mind, but it saw a decline during the middle years of the 20th century with the rise of logical positivism. The recent interest in the hard problem of consciousness has once again made panpsychism a widespread theory.