In concise terms

In concise terms, realism identifies patterns of behavior in a world that is apparent and objectively observable. This notion is rejected in constructivism which argues that the world is socially constructed and therefore, not objectively verifiable (Reus-Smit and Snidal, 2008). An inherent difference between the theories of realism and constructivism lies in the method through which they both approach the concept of ideas in the political world. Constructivism stresses that ideas take a central role in the world of politics, whereas realism is completely indifferent to its importance.

Despite the evident differences between the two outlooks, both constructivism and realism are not completely dissimilar. Both theories hold that states are the “fundamental actors in international politics” (Weber, 2014: 264). With regards to constructivism, this belief allows for the presence of non-state actors but places the greatest power in the constructed relationships between states in terms of the effect on the international structure. An additional shared feature between the two theories lies in an underlying commitment to an “epistemology indebted to positivism” which provides an outlook through which to understand the world (Fierke, 2016: 167).