The Biological approach to explaining abnormal behaviour assumes that the behaviour can be explained by physical factors. Hippocrates was a man who lived during the 5th century and is thought by many to be the father of modern medicine. He did not accept that evil spirits or astronomy were the causes of psychological disorders. Hippocrates believed that there were natural causes for the disorders and appropriate treatments could be found. He focused on the "four humors" of the brain. He believed that the four humours must be balanced for healthy mental states and when one humour was stronger, various disorders would appear. To balance the humors, Hippocrates would tell patients to change their lifestyles. There are now new ideas when talking about the biological explanations of psychological disorders. But, Hippocrates' focus on mental processes and clinical practice was a revolutionary concept.