This parameter considers the order of verbal affixes on transitive verbs of conscious, willful action. The term subject (Subj) is used here to refer to use the agent; object (Obj) to the patient. Verbal affixes are defined as morphemes that attach directly to the verb and indicate the person and/or class of the subject; the tense (T), aspect (A), and mood (M) of the verb; the relationship of the verb to its object[1]; the indirect object of the verb (Rec); and verbal voice (GV, for genus verbi). These morphemes may be analytic (monoexponential: one function expressed by a single morpheme) or synthetic (polyexponential: multiple functions expressed by a single morpheme). Affixes that serve a function that is not fully grammatical should not be considered in this parameter.[2] The parameter values that follow are not a complete list, but are instead meant to illustrate the ways in which Subj, T, A, M, Rec, and GV[3] can combine to show the orders in which monoexponential and polyexponential verbal affixes appear. Use of a dash (–) between functions indicates that they appear sequentially as separate affixes, while the tilde (~) indicates that the functions are served simultaneously by a synthetic affix.[4]
Types:
NoAff: Verbal functions are not expressed through the use of verbal affixes.
Subj–M–T: The following functions are expressed by verbal affixes, in the following order: person of the subject,[5] verbal mood, verbal tense.
M–T–Subj: The following functions are expressed by verbal affixes, in the following order: verbal mood, verbal tense, person of the subject.
Subj–T~A~M: The following functions are expressed by verbal affixes: person of the subject, tense, aspect, mood. These functions are marked by the use of two affixes: one appearing first, marking the person of the subject, and a second, synthetic affix simultaneously marking tense, aspect, and mood.
Subj–T~A~M–Obj: The following functions are expressed by verbal affixes: person of the subject; tense, aspect, and mood; and object marking. These functions are marked by the use of three affixes: one appearing first, marking the person of the subject; a second, synthetic affix simultaneously marking tense, aspect, and mood; and a third, appearing last, marking the object.
As seen here, verbal affixes that do not apply in the language should not be listed in the parameter value.[6] If the use of affixes depends on the given tense, person, etc.[7], the pattern listed should reflect the most complex form.[8]
[1] Object-marking affixes mark features of the object, such as person, number or definiteness.
[2] For instance, verbal prefixes that serve any degree of semantic function (such as indicating direction) should not be considered. The removal of verbal prefixes serving a semantic function, unlike the removal of purely grammatical verbal affixes, generally does not result in ungrammaticality.
[3] These functions should only be listed if they are expressed as verbal affixes. If GV appears as a zero morpheme (for example, active voice is not marked, while passive voice is indicated by the use of an affix), it should be listed in parentheses. The parameter value (GV)–Subj–M–T, for example, indicates that the first affix following the verb stem is GV when it appears as an explicit (not zero) morpheme.
[4] For example, the parameter value Subj~T describes a single affix that simultaneously marks the person of the subject and the verbal tense; Subj–T, on the other hand, describes two affixes, the person-marking affix appearing before the tense marker.
[5] For the purposes of this parameter, affixes marking person and number of the subject (agent) separately are not distinguished. Each combination of person and number (such as third-person singular, third-person plural) should be taken as a single affix, even if the language expresses these functions analytically.
[6] For example, the value Subj–T may indicate that either the functions A, M, and Obj do not exist in the language or that they are expressed by means other than verbal affixes.
[7] This may occur if the present tense is not marked by an affix, while the past tense is, or if explicit (non-zero) object-marking affixes only appear with definite objects.
[8] In most languages, third-person simple past forms (with object marking, if applicable) should be used to determine affix order.