The Russian novelist Vladimir Nabokov wrote an insightful article on the perils of literary translation, where he described the ‘three grades of evil’ that can befall a translation: errors due to ignorance or misguided knowledge, errors because the translator intentionally skips words or passages that might seem obscure or obscene, and beautification to conform to the notions and prejudices of a given public. In this seminar, I follow Nabokov’s ‘taxonomy of evil’ to analyse investment arbitration awards, in order to identify examples of interpretation practice. Arbitral tribunals have been accused of paying ‘lip service’ to the Vienna Convention on the Law of Treaties’ general rule of treaty interpretation as expressed in its Article 31. But, how good is the guidance provided by the Convention in avoiding the three grades of evil? The paper will argue that Article 31 leaves too much scope to the dangers of conformity to the notions and prejudices, not of the public at large, which was the concern of Nabokov as a novelist, but of the restricted public of investment arbitrations on the one hand, and of the arbitrators themselves on the other. Contextually, the incorporation in investment treaties of language developed in specific domestic frameworks (i.e. U.S. constitutional jurisprudence) will be presented as an example of semantic hegemony accompanied by hermeneutic conformity.