Number[erg]: number agreement with ergative argument
Number[erg]
Finite verbs in many Indo-European languages agree in person and number with their subject.
In Basque (a polypersonal language), certain verbs overtly mark agreement with up to three arguments: one in the absolutive case, one in ergative and one in dative. Thus in dakarkiogu “we bring it to him/her”, akar is the stem (ekarri = “bring”), d stands for “it” (absolutive argument is the direct object of transitive verbs), ki stands for the dative case, o stands for “he” and gu stands for “we” (ergative argument is the subject of transitive verbs).
Number[abs]is the number of the absolutive argument of the verb. The corresponding feature in Interset 2.041 is calledabsnumber.Number[erg]is the number of the ergative argument of the verb. The corresponding feature in Interset 2.041 is calledergnumber.Number[dat]is the number of the dative argument of the verb. The corresponding feature in Interset 2.041 is calleddatnumber.
One may want to use just Number instead of Number[abs].
However, there are two issues with that (at least in Basque).
First, the absolutive argument is not always the subject. For transitive verbs, it is the object, so the parallelism with nominative-accusative languages would be weak anyway.
Second, and more important, some Basque finite verbs have additional morphemes of nominal inflection.
Thus their form reflects the person-number agreement with the absolutive argument (nor), and nominal inflection (case, number etc.) at the same time.
Examples: dena (Number=Sing|Number[abs]=Sing),
dituena (Number=Sing|Number[abs]=Plur|Number[erg]=Sing),
dugunak (Number=Plur|Number[abs]=Sing|Number[erg]=Plur),
direnak (Number=Plur|Number[abs]=Plur).
So we reserve the Number feature for nominal inflection, and the Number[abs] feature for agreement.
Note that we also define Person[abs] and Polite[abs], although there is no direct conflict for these features.
But it is better to have these features aligned with Person[erg], Polite[erg], Person[dat] and Polite[dat].
Sing: singular ergative argument
Examples: [eu] dakarkiogu Number[abs]=Sing|Number[dat]=Sing
Plur: plural ergative argument
Examples: [eu] dakarkiogu Number[erg]=Plur