Punctuation is a worrisome thing, not the least because experts differ in their interpretation of its rules. Here we present the system we believe is most useful in business writing. You may encounter other opinions of what is “correct.” No matter. Be consistent with your own usage, and remember the cardinal rule: The purpose of punctuation is to help readers follow your meaning.
The apostrophe indicates omission, possession, and sometimes the plural of certain letters, nouns, numbers, and abbreviations.
1. The possessive pronouns—its, hers, his, ours, yours, theirs—do not use an apostrophe.
2. The possessive of plural nouns ending in “s” is formed by adding an apostrophe: 10 days' trial.
3. Joint possession ...