John watson; behaviourism, study behaviour and nothing else. Clinical applications; mental health, problem disorders, how to change their behaviour. Video game design; user experience, helping game designers the most enjoyable to players. Biological level, cognitive level, behaviour level, physiological level, each level provides its own insights. Early beliefs of the mind; early beliefs about mind and behaviour were grounded in spiritualism and mysticism. evil spirits were behind mental health problems. We don"t perceive absolute things, we perceive relative things, relation not absolute. Plato; ancient greece, the importance of logic and reasoning. Logic and reasoning allows for disproving and approving theories. Plato plays a role in moving thoughts from spiritual to more grounded in observation. The only way to come to absolute knowledge is by de nite conclusions. Believer in denying your senses to understand the world in a di erent way. Aristotle; disagrees with plato, the world is too detailed to lend itself to simple analytic details such as triangles.