If you use the definition of something — like a triangle — you can write a statement that is always true and always false.
Always true: If a polygon has three sides, then it is a triangle. Always false: If a polygon has three sides, then it is a square. Sometimes true: If it is the 24th of December, then you celebrate Christmas.
Practice makes perfect
To write a statement that is always true, we can use the definition of a triangle. It states that a triangle is a polygon with three sides.
If a polygon has three sides,
then it is a triangle.
Using that same definition, we can write a statement that is always false.
If a polygon has three sides,
then it is a square.
To write a statement in which the truth value depends on the person interpreting it, we can consider the fact that Europeans celebrate Christmas on the 24th of December while Americans celebrate Christmas on the 25th of December.
If it is the 24th of December,
then you celebrate Christmas.
This statement is true for a European, but false for an American.
