I took this sentence from the first part of the 5e SRD. From this sentence, I'm going to look into my APA style guide to look at their grammar and style rules. I first mark all of the nouns, the number, and the state of possession if need be.
Is a character (sing. noun) muscle-bound and insightful? Brilliant and charming? Nimble and hardy? Ability scores (comp pl. noun) define these qualities (pl. noun) —a creature’s (sing. pos. noun) assets (pl. noun) as well as weaknesses (pl. noun).First it would be great to review rules for plural nouns.
Plurality of Nouns (Notes from Chicago Style guide)
- General rule: For most common nouns, form the plural by adding s. For words ending in ch, j, s, sh, x, or z add es instead: character, characters; creature's is singular; asset, assets; weakness, weaknesses.
- For singular common words ending in consonant + y, make it plural by dropping the y and adding ies: baby, babies;
- For singular common words ending in consonant + f or fe, make it plural by dropping the f or fe and adding ves: dwarf, dwarves.
- For singular common words ending in ff, make it plural by adding a s: cliff, cliffs.
- For singular proper words, add a s: the Wickhams
- For compound words, add s or es to the last noun. This is the case for ability scores.
- In a prepositional phrase or adjective follows, add s or es to the main noun.
- For letters and numerals, form the plural by adding an s alone: Rs, 2s, 2010s. (APA agrees thought it also mentions the spelled numbers like fours, sixes, and threes)
- For letters that might create confusion and lower case letters, add an 's: i's, x's, y's, A's, B's.
- For abbreviations, add s: DVDs, RPGs. (APA agrees)
- Add an 's if the abbreviation has an internal period or lower case letter: PhD's.
- Irregular abbreviation plural: p. page, pp. pages; n. note, nn. notes. (APA agrees)
- Science unit of measurements: 1 m, 5 m. (APA agrees)
- Terms in italics, form the plural by adding an s in roman type: Two Scrolls of Infinitys
- Collective nouns vary in how they are used compared to British English. Most of the time in AmE, collective nouns are singular.