version 8 by Emily Short
Section: Ambiguously plural
We also create the term "ambiguously plural" to refer to items such as "pair of socks", "set of chessmen", "crew of pirates", etc., which the player might reasonably refer to as either "it" or "them". These items will then respond equally well to "it" or "them" in input.
The default Inform way of finding out whether something has a plural name is to say
if the noun is plural-named
But if we also wish to test for things that are ambiguously plural, we have a new phrase
if the noun acts plural
which looks for both plural-named and ambiguously plural items.