Prefixes are groups of letters that are added to the start of words to change their meaning.
Most prefixes mean a similar thing when they're added to different words.
For example: unhappy, unlocked, unfair and intolerant, incapable, inconsiderate
For example: disagree, disobey, misbehave, mislead
For example: redo, reappear, redecorate
For example: subheading, submarine
Remember: 'Root words' are the basic words that are used to form other words. Root words haven't had any prefixes or suffixes added to them yet.
Not all prefixes can be added to all root words. You have to choose the correct one.
For example: un- can be added to 'happy' to make 'unhappy', but dis- or mis- couldn't.
Adding in- can be particularly tricky. There are three rules to remember.
1. When the root word begins with an l, the prefix in- changes to il-.
For example: il + legal = illegal
2. When the root word begins with an r, the prefix in- changes to ir-.
For example: ir + regular = irregular
3. When the root word begins with an m or a p, the prefix in- changes to im-.
For example: im + possible = impossible