Affect vs Effect
The best way to tell these two apart is to remember that one is a verb (affect) and the other a noun (effect). Affect is an action word, as in the things we say can affect the people close to us, or the weather can affect our mood. The result of those actions is the effect. For example, too much coffee can have a negative effect on your body.

Advise vs Advice
This is another example of two words that sound alike, but one is something we do (advise) and the other is an abstract noun and the direct result of that action (advice). To advise someone is to help them with a problem by offering suggestions or solutions; the suggestion itself is a piece of advice.

Compliment vs Complement
Be extra careful with these two words because both can be used as a verb (action words) and have positive connotations. A compliment is a positive statement about someone or something, and when you compliment a person, you are telling them how much you like their new hairstyle or dress, for example. But to complement something is to match or enhance it, similar to how white wine complements a seafood dinner.

Principle vs Principal
These two homonyms – words that sound the same but are spelled differently and have different meanings – are frequently mistaken for one another. Both are nouns, but principle is an abstract noun and refers to a code of ethics the foundations of a belief system. Principal, however, is the head of a school.

They’re vs Their, You’re vs Your
Arguably the most common errors made in English writing involve one of these homonyms, and even native speakers are known to use them incorrectly! The best way to avoid this is by remembering that they’re and you’re are contractions of they are and you are, respectively, as in “They’re (they are) going to be late” or “You’re (you are) welcome.” Meanwhile, their and your – without the apostrophe – are possessives to show that something belongs to someone: “My friends forgot to bring their swimsuit” or “Can I borrow your book?”

We hope these explanations have cleared up any confusion or lingering vocabulary questions you may have. The next time you are unsure of which of these words to use, remember to check the British Council Indonesia’s English Success Tips for help!