Valency-changing operation

Definition
Valency-changing operation is a syntactic and/or morphological operation due to which the relationship between a verb and its arguments is changed.

Example
Due to the operation of passive formation, the internal argument of transitive verbs in the active voice gets externalized, while the external argument becomes an (optional) adjunct: John killed his mother vs. His mother was killed (by John)).

Links

 * Utrecht Lexicon of Linguistics