The not operator inverts a boolean value: python not True # False not False # True Use not to flip a condition: python if not logged_in: print("Please log in") if not (age >= 18): print("Too young") # Same as age < 18 Be careful with parentheses. not age >= 18 is parsed as (not age) >= 18, which doesn't make sense.
Use not (age >= 18) to invert the whole condition. Often, rewriting without not is clearer: if age < 18 instead of if not (age >= 18).