We present a descriptive generalisation according to which a verbal or an event argument is merged as an indirect object (IO) when the direct object (DO) position is occupied. Our goal is to formalise this generalisation and to show how current syntactic theory provides the necessary tools to support it. Specifically, the converging consensus that all so-called intransitive verbs have an internal nominal argument resolves previous exceptions to the generalisation and shows that the transitivity restriction on thematic IOs is structural.