The challenging relationship between Legality of investment and Clean Hands Doctrine in International Investment law: can “the Aristotle’s Square of Oppositions” fix the challenge?

Abstract

The relationship between "Clean Hands Doctrine" and "Legality of Investment" in international investment law is a challenging one. So far, the actors in the process of foreign investment like states, Tribunals or organizations have paid attention to the relationship in various ways; As the approach of states in concluding bilateral investment treaties (BITs) has shown that these two concepts are different. In its latest 2023 analysis of investment arbitration cases, UNCITRAL made it clear that proving the Legality of Investment requires the Clean Hands Doctrine. According to some jurists, they are similar words. Therefore, it is obvious that so far international investment law hasn’t been able to reach a consensus. Hence, the goal of this article is to answer the question, what is the relationship between Legality of Investment and Clean Hands Doctrine? In current study, with a quantitative and qualitative approach, I analyzed Russia and Iran's bilateral investment treaties, as well as investment awards and opinions of jurists and came to the conclusion that “the Aristotle’s Square of Oppositions” can well analyze various approaches regarding the relationship between Clean Hands Doctrine and the legality of investment.  Ultimately, the "Venn Diagram" which was presented based on Aristotle's third and fourth propositions, i.e. the propositions "Particular affirmative" and "Particular negative" in the 19th century, can solve the current challenge.