The author compares the practice of trade and investment adjudicators in relation to the requirement to interpret a treaty ‘in the light of its object and purpose’. He begins by identifying a range of issues and choices that adjudicators are confronted with in this regard, and the practical barriers to any significant degree of judicial interaction or cross-fertilization between trade and investment adjudicators with respect to those issues. He then shows that notwithstanding the absence of judicial interaction, there is a remarkable degree of convergence in the legal reasoning of trade and investment adjudicators on diverse issues. Among the issues, he includes the basis for identifying a treaty's object and purpose, the need to balance competing objectives, the recognition of some of the limitations of purposive reasoning, and even standard forms of consequentialist arguments. The final section argues that such convergence is most easily explained by the theory that many aspects of legal reasoning and treaty interpretation derive not from knowledge of prior precedent and judicial practices, but from common sense and the nature of the judicial function.