1. Keep the base word intact:
* Most prefixes don't change the spelling of the base word: *un- + happy = unhappy; *pre- + pay = prepay
* Exceptions: *il-, im-, ir-, in-** often change the first letter of the base word to match its sound: *il- + legal = illegal; *im- + possible = impossible; *ir- + rational = irrational; *in- + correct = incorrect
2. Doubling consonants:
* If the prefix ends in a consonant and the base word begins with a consonant, double the consonant: *mis- + spell = misspell; *sub- + standard = substandard
* This rule doesn't apply if the prefix ends in a vowel: *re- + appear = reappear; *pre- + approve = preapprove
3. Dropping or adding letters:
* Sometimes, a letter is dropped from the base word: *dis- + appear = disappear
* Sometimes, a letter is added to the base word: *in- + hospitable = inhospitable
4. Specific Prefix Rules:
* *de-* often changes to *di-* before a vowel: *di- + articulate = diarticulate
* *re-* sometimes changes to *ir-* before a vowel: *ir- + regular = irregular
5. Consult the dictionary:
* When in doubt, always consult a dictionary! It is the ultimate authority on spelling.
Remember: There are exceptions to every rule, and spelling can be tricky. Practice and careful attention to detail are key.