What happens if you have a written phrase like
We were looking at the same poster(s).
but with a noun that has an irregular plural? E.g. with baby/babies, would this be the correct form?
We were looking at the same baby(ies).
Or, as a more exotic case:
We were looking at the same matrix(???). (plural is matrices)
Is there a rule or guideline for this?
It's not pretty, but the most common way I've encountered is to list both words, without the parentheses, with either a slash or the word "or" between them:
We were looking at the same baby/babies.
We were looking at the same matrix or matrices.
You can also try "baby (babies)", or reword in some way that avoids the question, or if the context permits, just use the plural.
The simple plural, those formed only by an addition of an "s", is the only case in which the parentheses are used to indicate the indeterminate plurality, as in "poster(s)". In all other cases, the alternatives are both given, separated by an "or", as in "the same baby or babies". (This can also be done for the simple case: "the same poster or posters" is acceptable, and may even be preferred in more formal writing.)
Write the singular and the plural of the word separated from a slash, as in baby/babies. I don't think there is a shorter way to write it, if not writing only the plural or the singular word.
I think it depends on how avant-garde your audience(s) is. I think connotatively most people who don't need a laxative(s) would get and appreciate the shorthanded form using matrix(ices). Don't be such a baby(ies).
