Here's why:

* Solid: Solids have a definite shape and volume. A feather maintains its shape and takes up a specific amount of space.

* Liquid: Liquids take the shape of their container, but have a fixed volume. A feather doesn't change its shape based on its container.

* Gas: Gases have no definite shape or volume and fill the entire container they are in. A feather does not behave like this.

Let me know if you have any other questions!