In this article data are presented from the Amele language and a number of other different Papuan languages to show that in these languages the medial verb form is marked for a binary distinction of realis versus irrealis modality. Furthermore it is demonstrated that in these languages the realis-irrealis distinction interacts with categories of tense and mood marked on the fina! verb in such a way as to divide them into the two basic domains of realis and irrealis modal status. It is also demonstrated for two of the languages (Amele and Nobonob) which have sentence particles with an illocutionary force function that these particles do not interact with the realis-irrealis modal system marked on the medial verb. In the final discussion and conclusion a schema is suggested to account for the facts of future tense, imperative mood and counterfactual mood being categorized as irrealis in these languages. The schema suggests that events can be referred to in the unreal world as either events that are potentially true/false in the real world, or events that used to be true/false in the real world, or events that are not true/false in the real world.