A general introduction to middle constructions can be found in Ackema & Schoorlemmer (2006). The middle constructions discussed above correspond to what Ackema and Schoorlemmer call "type I middles". Ackema & Schoorlemmer's study also reviews a number of theoretical approaches to the derivation of middle constructions and compares middles with a number of constructions that can readily be confused with them like inchoative unaccusative and easy-to-please constructions (the latter of which, unfortunately, seem to be mixed up with modal infinitives occasionally). Our discussion on regular middle constructions is further based on Keyser & Roeper (1984), Paardekooper (1986), Fagan (1988/1992), Levin (1993), Hoekstra & Roberts (1993), Ackema & Schoorlemmer (1994/1995) and Hulk & Cornips (1996). Discussions of impersonal and adjunct middles can be found in Hoekstra and Roberts (1993) and Ackema and Schoorlemmer (1994). A brief section on the reflexive middle can be found in Everaert (1986/1990), while the Heerlen Dutch cases are discussed in Cornips (1994/1996) and Cornips & Hulk (1996). We did not pay much attention in this section to the longstanding question as to whether the external argument of the input verb is syntactically realized in middles. The reason is that Ackema & Schoorlemmer (2006:184-191) have shown that the traditional tests for detecting implied agents (like control and binding) provide less than reliable results in the case of middles.