Art can be defined in many ways and encompasses a wide variety of mediums. Traditionally, art has fallen into three main categories: art as representation which copies or imitates something beautiful or meaningful; art as an expression of emotion to evoke responses in viewers; and art as form which is judged solely based on aesthetics and design principles. Key principles of art and design that help create unity and harmony include balance, rhythm, and harmony. Ultimately, art is subjective and anything that stirs emotion can be considered art.