This chapter tackles the issue of interpretation from the point of view of motion and time, mainly motion as change in space-time (kata topon kai chronon metavole), which depending on the interpretation could lead to an increase (auxesis), diminution (meiosis) of the treaty. This is mainly evidenced through the concepts of the principle of contemporaneity and evolutionary interpretation, and the chapter proceeds to demonstrate that the choice between these two is dependent on the ‘time-will’ of the parties. However, even evolutive interpretation has its limits and should never lead to an alteration (alloiosis) of the treaty. This chapter also analyses the rules of interpretation themselves, ie whether interpretative rules are constants, immutable and perennial ones, in the system of the law of treaties or whether they are, as any other rule, potentially susceptible to motion through time and change. This chapter demonstrates the false premise of the immutability of the rules of interpretation, and elaborates on the consequences of this to the choice between contemporaneous (static) and evolutive interpretation.