This chapter provides an overview of the properties of a particular type of diathesis alternation known as the
middle
. The most salient property of a middle is that the internal argument of the verb appears as the subject of the construction, as in a passive. The semantics of a middle differs from that of passives in that middles cannot be episodic, but are generic statements about the subject. In the first part of the chapter, middles are compared with a number of other diathesis alternations that are similar in their structure and/or semantics. This comparison teases out the properties that set middles apart as a distinct category. It is shown that two different types of middle should be distinguished. In one type, the middle is parasitic on a passive construction in the language; in the other type, the verb retains its active form. In the second part of the chapter, possible analyses of the middle are discussed. Two distinct types of analysis are discussed, one in which the rules linking argument structure to syntactic positions allow for some flexibility, and one in which the middle results from a purely syntactic derivation.