Aristotle believes that psychology is a part of natural science. He wrote Reflections on Black People and translated it into On the Soul. He divided souls into three categories: plants only have growing souls, animals have emotional souls and people have rational souls. Aristotle believes that people not only have special senses such as eyes, ears, nose and tongue, but also "ordinary senses" that perform intermediate functions above special senses and under abstract thinking. Aristotle divided psychological functions into two categories: cognition and motivation.