Neo means new. When neo appears before any theory, it means that the particular theory with the prefix Neo is an updated version of its classical theory. Neo also means recent, modification, or revival.
For example, in International Relations, we study theories like Neoliberalism, Neo-Realism, etc. These theories are essentially the revival or modified forms of classical liberalism and classical realism.
For example, classical realism held that people are selfish by nature therefore they compete for domination and self-advantage. Thus, world politics is a struggle for power that leads to anarchy on the international stage. However, Neorealism holds that human behavior and motivation are not guided by their inner selfishness; rather they are guided by the setting and environment in which the actors are situated.
In short, classical realists sought to explain state behavior by examining assumptions about people’s motives at the individual level of analysis; while neorealism emphasized the global level of analysis. Both the theories have the same idea of conflict or anarchy in international relations but with different underlying reasons for it.
In a similar way, all the other neo-theories are updated versions of classical theories. In other words, with tweaks in the classical theory emerged its modified form with neo as a prefix. All the neo-theories have an essence of their classical version with modification in underlying assumptions/hypothesis/basis.
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