ABSTRACT
Defining and theorizing migration is a challenging academic field. Since the second half of the 19th century, various academic disciplines such as demography, geography, economy, sociology, psychology and political science began to discuss the phenomenon of migration. The research works of E.G. Ravenstein in 1885 discovered that people migrate in order to improve living standards. However, various studies show us that theories and definitions of migration affect economic, political, cultural, philosophical, technological, and other aspects of human life. Various theories have tried to analyse the causes of migration: however, developing a migration theory or various migration theories presupposes terminological clarifications. Anthony Messina and Gallya Lahav have pointed out some important concepts that would better help us understand and develop migration theories. They define concepts such as international migration, immigration, emigration, immigrant and migrant workers, seasonal migrants, family reunification, illegal or irregular migrants, overstayer, undocumented worker, undocumented immigrant, forced or involuntary migration, refugee, asylum seeker and non-refoulement. These definitions affect not only academic theorization, but also political decisionmaking calculations. Departing from their theoretical definitions of these concepts Messina ampentity Lahav specified four major components of migration: labour migration (permanent and temporary), family reunification, humanitarian or forced migration (asylum seekers and refugees), and illegal migration. 1
