The problem of consciousness is related to one of the oldest questions of philosophy: what does the world consist of? Who am I? This is in principle related to the mind-body problem: what is the relationship between the physical and the mental? Solutions to this problem can be distinguished in monistic theories, which suggest that there are one kind of things in the world, and dualistic theories, which suggest that there are two kinds of things. Monistic theories assume that the world consists of only one kind of matter (body or mind). Examples of supporters of these monistic theories are the materialists. In dualism it is a combination of matter (the body) and spirit. The most famous dualist is René Descartes. There are two types of dualism, namely, knowledge of dualism and substance dualism. The term "psychology" first appeared in the eighteenth century to describe the philosophy of mental life, but it was towards the end of the nineteenth century when psychology was seen as a science. Important psychologists during this period were James, Wundt and Freud. After that behaviorism came under the direction of Watson, who saw psychology as a natural science that should have the goal of predicting and influencing behavior. Chalmers states that the ambiguities about consciousness can be divided into easy problems and hard problems. Qualia are private qualities, the way someone experiences an experience. Conscious experiences consist of qualia and the problem of consciousness can be reformulated in terms of how the qualia are related to the physical world or how objective brains produce subjective qualia. To investigate whether qualia can have added value, thought experiments such as Mary's experiment and the experiment of the philosophy zombie can be used. Different...