UPSC and IAS Mains - Is Psychology a good optional subject. Psychology is an optional subject that is reasonably popular among IAS aspirants. It may not be as popular as history or public administration, but it still fares better than many other subjects. So you will find that the laws in psychology are not as precise. Psychology is the science of behaviour and mind, including conscious and unconscious phenomena, as well as feeling and thought. It can be defined as the “scientific study of the human mind and its functions, especially those affecting behaviour in a given context.” It is a science although some of the theory borders on the philosophical.