The property Auxiliary Selection has the value “yesâ€ when the language has an active perfect aspect (or past tense) that makes use of a past participle and an auxiliary verb where the auxiliary verb alternates between "have" or "be" depending on various factors. Some factors known to influence auxiliary selection include verb class (unergative versus unaccusative), transitivity, and person features of the subject.<br><br>

<b>NA (Not Applicable)</b>: This property is defined for a language only if: (a) the language has main verb "have", (b) the language uses auxiliary verbs in the formation of the perfect (past). Otherwise, the language is NA for this property.<br><br>

Examples:<br><br>

1. <br>
Italian is "yes" for Auxiliary Selection, since the intransitive verb "telephone" 
takes a different auxiliary verb from the intransitive verb "arrive" in the past.<br><br>

Gianni ha/*è telefonato<br>
G.       has/*is telephoned<br>
"Gianni called."<br><br>

Gianni è/*ha   arrivato<br>
G.       is/*has arrived <br>
"Gianni arrived."<br><br>

2.	<br>
English is “noâ€ for auxiliary selection since English expresses the perfect with the verb “haveâ€, but it never expresses the perfect with the verb “beâ€:<br><br>

John has left.<br>
*John is left.<br>
(* means ungrammatical)

