A discipline is focused study in one academic field or profession. A discipline incorporates expertise, people, projects, communities, challenges, studies, inquiry, and research areas that are strongly associated with a given discipline. For example, the branches of science are commonly referred to as the scientific disciplines, e.g. physics, and Gravitation is strongly associated with that disciplinary knowledge. Individuals associated with academic disciplines are commonly referred to as experts or specialists. Others, who may have studied liberal arts or systems theory rather than concentrating in a specific discipline are classified as generalists. While disciplines in and of themselves are more or less focused practices, scholarly approaches such as multidisciplinarity, interdisciplinarity, transdisciplinarity, and crossdisciplinarity, integrate aspects from multiple disciplines, therefore addressing any problems that may arise from narrow concentration within specialized fields. For example, professionals may encounter trouble communicating across disciplines because of differences in language and/or specified concepts. Some researchers believe that academic disciplines may be replaced by what is known as Mode 2 or "post academic science", which involves the acquisition of cross-disciplinary knowledge through collaboration of specialists from various fields.