Hyphens are used in various cases, including:
1. Compound Words: To join two or more words that function as a single adjective before a noun (e.g., well-known author, high-speed train).
2. Prefixes: When a prefix is added to a word and would create confusion without a hyphen (e.g., re-enter, co-worker).
3. Numbers: To spell out numbers twenty-one to ninety-nine (e.g., twenty-three, sixty-seven).
4. Fractions: When writing out fractions (e.g., two-thirds, three-fourths).
5. Compounds with Prefixes: In cases where a hyphen clarifies the meaning or eases reading (e.g., non-native, pre-existing).
6. Joint Adjectives: When two or more adjectives together describe a noun (e.g., a well-dressed man).
7. Hyphenated Last Names: In compound last names (e.g., Smith-Jones) or when one part of a last name is separated (e.g., Mary Johnson-Smith).
8. Avoiding Ambiguity: To prevent confusion or misinterpretation (e.g., man-eating shark vs. man eating shark).
Hyphen usage can vary depending on style guides and specific words. Always consult a dictionary or style guide for precise rules on hyphenation.