important aspect of Tesnière's understanding of valency was that the subject is an actant (=argument, complement) of the verb in the same manner that the object is. The concept of subcategorization, which is related to valency but associated more with phrase structure grammars than with the dependency grammar that Tesnière developed, did not originally view the subject as part of the subcategorization frame, although the more modern understanding of subcategorization seems to be almost synonymous with valency. Changing valency Most languages provide a means to change the valency of verbs. There are two ways to change the valency of a verb: reducing and increasing. Note that for this section, the labels S, A, and P will be used. These are commonly used names (taken from morphosyntactic alignment theory) given to arguments of a verb. S refers to the subject of an intransitive verb, A refers to the agent of a transitive verb, and P refers to the patient of a transitive verb. (The patient is sometimes also called undergoer or theme.) These are core arguments of a verb: Lydia (S) is sleeping. Don (A) is cooking dinner (P). Non-core (or peripheral) arguments are called obliques and are typically optional: Lydia is sleeping on the couch.Don is cooking dinner for his mom. Valency-reducing Reducing valency involves moving an argument from the core to oblique status. The passive voice and antipassive voice are prototypical valency reducing devices. This kind of derivation applies most to transitive clauses. Since there are two arguments in a transitive clause, A and P, there are two possibilities for reducing the valency: 1. A is removed from the core and becomes an oblique. The clause becomes intransitive since there's only one core argument, the original P, which has become S. This is exactly what the passive voice does. The semantics of this construction emphasizes the original P and downgrades the original A and is used to avoid mentioning A, draw attention to P or the result of the activity. (a) Don (A) is cooking dinner (P). (b) Dinner (S) is being cooked (by Don). 2. P is removed from the core and becomes an oblique. Similarly, the clause becomes intransitive and the original A becomes S. The semantics of this construction emphasizes the original A and downgrades the original P and is used when the action includes a patient, but the patient is given little or no attention.