Sentences that contain a predicate verb may express the agent (conscious, willful performer of action) in a number of ways. In some languages, the agent cannot be marked without an explicit pronoun or noun. Other languages allow marking of an implicit agent, relying on verb-dependent strategies such as verbal agreement, as well as verb-independent items. Use of these strategies may be (fully or partially) required or optional. To classify a language in terms of this parameter, first and second person should be examined.
Types:
NPPonly: Marking of the agent is only possible with an explicit pronoun or noun; no other morphological or lexical strategies exist.[1]
NPPobl: Marking of the agent requires an explicit noun or pronoun, but other lexical or morphological strategies exist.[2]
NPPnonobl: The agent may optionally be marked with an explicit pronoun or noun.[3]
NPPor: The agent may only be marked lexically or morphologically if it is not already marked by an explicit pronoun or noun.[4]
NPP: The agent is marked lexically or morphologically, optionally accompanied by an explicit pronoun or noun.
Agr: Morphosyntactic agreement on the verb[5] is used to mark the agent.
Clit: A clitic[6] is used to mark the agent.
Aux: An auxiliary (distinct from the lexical verb, and also able to express other grammatical categories[7]) is used to mark the agent.
Clsfr: A classifier is used to mark the agent, which occurs simultaneously alongside the expression of verbal class.
When a language displays more than one type of marking, two values can be listed. If one type is structurally dominant, a slash (/) can separate the two values, with the dominant value appearing first; if neither is dominant, the two are listed with an ampersand (&) separating the two, while the use of a plus sign (+) instead of an ampersand indicates that the two strategies must be used simultaneously. Optional strategies are listed within parentheses.
[1] This is also true of sentences in which the agent is the speaker and the listener is the object. For NPPonly languages, the use of explicit pronouns, nouns, or proper names is required broadly; no grammatical features, such as morphological agreement, identify the subject or object. (Therefore, the value NoPM is the only possibility for the parameter Person agreement on the verb.) If there exists at least one person or number in which another agent-marking strategy is possible, however, the language should not be classified as NPPonly.
[2] Through the use of a plus sign (+), this value should be paired with another value.
[3] Through the use of a plus sign (+), this value should be paired with another value. For example, pro-drop languages, which use inflected verbs to mark the agent without a pronoun, are described as NPPnonobl+AgAgr.
[4] Through the use of a plus sign (+), this value should be paired with another value.
[5] Such strategies include affixation, internal flexion, and agent-specific dependent pronouns. If this value applies, the language is automatically restricted from the NoPM and PPM values for the parameter Person agreement on the verb.
[6] Clitics are characterized by the fact they do not obligatorily attach to the verb directly.
[7] These may include tense, aspect, and mood.