opinio iuris → συνείδηση δικαίου
Opinio juris sive necessitatis ("an opinion of law or necessity") or simply opinio juris ("an opinion of law") is the belief that an action was carried out because it was a legal obligation. This is in contrast to an action being the result of different cognitive reaction, or behaviors that were habitual to the individual. This term is frequently used in legal proceedings such as a defense for a case.
Opinio juris sive necessitatis - Wikipedia