(grammar) A middle voice construction is a lexical, morphological, or syntactic construction that functions to express an inherently transitive event as a process undergone by a PATIENT with no reference to an independent AGENT.
English has no morphological middle voice category, but does have lexical middle verbs and syntactic middle voice constructions.
1. active voice: Dennis broke the window.
2. passive voice: The window was broken (by me).
3. lexical middle voice: The window broke.
Example 3 may be considered lexical middle voice because it is a feature of the lexical meaning of the verb to break. Not all verbs can be used this way, e.g., The ball kicked cannot mean that the ball is the undergoer of the act of kicking.
4. active voice: I drive this Volvo.
5. passive voice: This Volvo is driven (by me).
6. syntactic middle voice: This Volvo drives like a tank.
Example 6 may be called a syntactic middle construction because it requires an adverbial adjunct of some kind. In the example, the adjunct is like a tank. Other examples are: These trousers wear well, This soup eats like a meal etc. Without the adjunct, such constructions are odd at best: ?These trousers wear, ?This soup eats.
In languages with more grammatical categories expressed via verbal morphology (such as ancient Greek and Icelandic), middle voice may be expressed morphologically via a verbal inflection. English accomplishes the same functions lexically or syntactically, consistent with its general typological characteristics.