Here's why:

* Liquids have a definite volume but take the shape of their container. Ink, when stored in a bottle, maintains its volume but will flow and take the shape of whatever container it's poured into.

* Gases have no definite shape or volume and expand to fill their container. Ink doesn't behave this way.

* Solids have a definite shape and volume. Ink, while it can dry and solidify, is primarily a liquid in its functional state.

* Plasma is a superheated gas where electrons have been stripped from atoms, creating a highly charged state. Ink is not plasma.