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What are the rules on where to put apostrophes?

Answer:
Apostrophes are put in place of elided letters, e.g. don't, for, do, not, or fo'c's'l for forecastle. In the case of possessives, the rule is: 1) All singular nouns, regardless of spelling, take 's; 2) Plural nouns ending in s take the apostrophe alone, but plurals not ending in s take 's. For example, Russ's house, States' rights, women's sports.
First answer by ID1206120401. Last edit by Cosmo the gaylord. Contributor trust: 2 [recommend contributor recommended]. Question popularity: 8 [recommend question].