When do you use prettier or prettiest in a sentence?

You use "prettier" when comparing two or more things, and "prettiest" when you're identifying the most beautiful thing in a group.

Here are some examples:

Prettier:

* "This dress is prettier than the one I wore yesterday."

* "The sunset was prettier than I imagined."

* "The blue car is prettier than the red one."

Prettiest:

* "She is the prettiest girl in the class."

* "That is the prettiest flower I've ever seen."

* "This cake is the prettiest one I've ever baked."

Remember: "Prettier" is a comparative adjective, used when comparing two things. "Prettiest" is a superlative adjective, used when comparing three or more things and identifying the most beautiful.