This section discusses a second type of verb-frame alternation involving the external argument of verbs, usually called middle formation. The middle is one of three voices typically found in the Indo-European language family: active, middle and passive. Whereas passivization involves the demotion of the external argument to adjunct status, middle formation involves the complete removal of the external argument from the verb frame, as is clear from the impossibility of adding an agentive door-PP to the middle construction in (154).

Middles are further characterized by the absence of a specific time reference, in the sense that the constructions refer to an individual-level property of their subject, and by the fact that they contain an evaluative modifier like moeilijkwith difficulty or gemakkelijkeasily. Middle formation can be divided into four main types: regular, adjunct, impersonal and complex reflexive middles; cf. Ackema & Schoorlemmer (2006/2017). Section 3.2.2.1 will first briefly characterize these four subtypes and identify a number of properties that they all share. Sections 3.2.2.2 to 3.2.2.5 will discuss the four main types in more detail.