1. Hyphenation:
* Compound words: This is the most common use. Hyphens are used to connect two or more words that act as a single unit. This can include:
* Adjectives: "well-known", "high-quality", "state-of-the-art"
* Nouns: "mother-in-law", "sister-in-law", "go-between"
* Verbs: "check-in", "hand-wash", "break-dance"
* Numbers: Hyphens are used to connect numbers between 21 and 99: "twenty-one", "forty-two", "seventy-eight".
* Prefixes: Hyphens are often used when a prefix is followed by a capitalized word or a number: "pre-Columbian", "anti-American", "mid-19th century".
2. Avoiding ambiguity:
* When words could be misinterpreted: "re-sign" (sign again) vs. "resign" (quit), "man-eating" (eating men) vs. "man eating" (a man who is eating)
3. For clarity:
* With compound words: Sometimes a hyphen is used to make a phrase clearer, especially with longer compound words: "self-service" vs. "self-conscious"
4. With compound modifiers:
* Before a noun: Hyphens are used to connect words that function as a single adjective before a noun: "high-speed train", "state-of-the-art technology", "well-known author".
Note: Hyphenation rules can be complex and vary depending on the style guide being followed. If you're unsure, it's best to consult a dictionary or style guide.