In this article, I reconstruct Kazimierz Ajdukiewicz’s view that he called radical conventionalism (as opposed to moderate conventionalism developed by Henri Poincaré and Pierre Duhem). Then, I recall little‑known criticism of this approach developed by Stefan Amsterdamski. Finally, I demonstrate, contrary to the conception of the originator’s declarations, that a radical conventionalism is not a ‘paper fiction’. On the other hand, the standpoint of radical conventionalism is useful due to the precision of expressions provided to it by Ajdukiewicz; it shows the difficulties that have to be tackled by each philosophical approach assuming a social constructivism or related notion.