For most English words, the rules for construction of possessive forms are fairly simple.
Singular nouns are possessivised by adding -’s to the end (even if the word already ends with an S):1
- cat → cat’s
- bass → bass’s
- CVR → CVR’s
Most plural nouns are possessivised by adding a lone apostrophe after the -s, -es, or -ses taken upon pluralisation:
- APU → APUs → APUs’
- Jones → Joneses → Joneses’
- bus → busses → busses’
Pronouns have special possessive forms, which do not use apostrophes (her, his, their, hir, our, your, my, its, etc.).
However, not all English nouns are pluralised simply by adding an -s, -es, or -ses to the end (although, for some of these, an -s/-es/-ses form, although not the usual method of pluralisation, is still available as an alternate plural form). All have possessive forms that include an S somewhere, as is obvious when listening to spoken English, but, for some, the shape this takes in written English is far from clear.
If the plural form is irregular, but does still end in an S, the possessive is formed by adding an apostrophe to the end:
- octopus → octopodes → octopodes’
If the normal plural is the same as the singular, and an -s/-es/-ses form is available as an alternate plural, the possessive is formed by tacking on an apostrophe to the end of the -s/-es/-ses form:
- fish → fish [alternate plural fishes] → fishes’
For many, however, the normal plural alters the stem of the noun in a manner not present in the singular or the alternate -s/-es/-ses form, or there is no -s/-es/-ses form available at all, even as an alternate, giving rise to a couple of annoying corner cases:
- minimum → minima [normal plural] → ...?
- minimum → minimums [alternate plural] → minimums’
- aircraft2 → aircraft → ...?
I can think of a few possible ways of possessivising these irregular -s/-es/-ses-less plural nouns (but all have serious problems):
- Adding -’s onto the end, as one would do for a singular (applies a singular form, rather than a plural form, to a plural noun):
- minimum → minima → minima’s?
- aircraft → aircraft → aircraft’s?
- Adding a lone apostrophe onto the end, as one would do for most plurals (inconsistent with spoken English, as it fails to produce the terminal S that is evident in speech, requiring that a phoneme that is both present and audible be rendered invisible on the page):
- minimum → minima → minima’?
- aircraft → aircraft → aircraft’?
- Adding -s’ onto the end (effectively pluralises the noun twice over):
- minimum → minima → minimas’?
- aircraft → aircraft → aircrafts’?
Which of these methods, if any, is the correct one for generating the plural possessive forms of these irregularly-pluralised nouns?
1: Possessivisation of nouns is one of only two uses for apostrophes anywhere in the English language (the other being the formation of contractions, like don’t and wouldn’t’ve).
2: A word of special importance for someone who spends a large portion of her time over at Aviation.SE!