Here's a breakdown of the reasons:
* Preventing Misinterpretation: Hyphens can prevent misreading. For example, "small-town" is different from "small town." Without the hyphen, it could be read as "a small town" instead of "a town that is small."
* Joining Modifiers: When a compound word modifies a noun, hyphens often make the meaning clearer. For instance, "a well-known author" is more easily understood than "a well known author," which could be mistaken for "an author who is well known."
* Indicating a Single Unit: Hyphens can indicate that two words function as a single unit, especially when the compound word is a noun or adjective. For example, "a mother-in-law" is a single person, while "a mother in law" could refer to multiple individuals.
* Consistency and Style: Hyphens also follow style guidelines and conventions. Different dictionaries and style guides have rules for when to use hyphens in compound words.
However, it's important to note that:
* Hyphen use is not always consistent. Some words that were once hyphenated are now commonly written as single words (e.g., "email," "website").
* Hyphen use can vary depending on the context and the meaning intended.
Ultimately, the best way to determine whether a compound word should be hyphenated is to consult a dictionary or style guide.