This article analyses the relationship between the tribunal's initiative and the arguments made by the parties. It examines to what extent a tribunal may or shall integrate or develop arguments that should have been made by the parties, both in respect of questions of fact and in respect of questions of law. It briefly explains the question of how active the tribunal may be in respect of the arguments made by the parties. This article discusses that the power of the tribunal is ultimately limited by the rules on jurisdiction and any mandatory rules of procedure contained in the applicable international investment treaty and by the criteria for determining the validity and enforceability of an arbitral award. It argues that the tribunal enjoys considerable freedom in respect of the inferences that it draws from the evidence and in respect of the legal consequences of the proven facts. This article concludes by analysing that the tribunal's own inferences and arguments should be communicated to the parties.