General Rules
* "Un-" is the more common prefix: It's used in a wider range of words and is generally the default choice.
* "Dis-" is often used before words of Latin origin: This is especially true for words related to "dis-" meaning "apart" or "away" (e.g., "disengage," "disassemble").
* "Un-" can be used with words of both Latin and Greek origin: This is the case for many common words like "unhappy," "unaware," and "unfold."
Exceptions
There are many exceptions to these general rules, and sometimes usage is just based on convention.
* "Dis-" can be used even when the word isn't of Latin origin: For example, "disagree," "disapprove," and "disappear."
* "Un-" can be used with words of Latin origin: For example, "uncertain," "unnatural," and "undo."
Examples:
* "Un-" : unhappy, unable, unbreakable, untie, unwrap
* "Dis-" : disagree, disapprove, disappear, disallow, disband
Tips for Choosing
1. Consider the origin of the word: If the word is Latin, "dis-" might be more likely.
2. Check the dictionary: If you're unsure, look up the word in a dictionary.
3. Use the most common option: If both prefixes work, "un-" is often the safer choice.
4. Pay attention to the context: Sometimes the meaning of the word suggests one prefix over the other.
Remember that English is a complex language, and there are always exceptions to the rules. If you're ever unsure about a particular word, it's always best to check a dictionary or consult a grammar guide.