Abstract art describes a broad category of artwork in which forms and figures are not depicted realistically. An abstract work of art may not depict anything recognizable at all. The invention of photography in the 19th century replaced painting as the primary means to capture reality. This freed avant-garde painters like the Expressionists to explore a more personal, spiritual reality and to experiment with the formal aspects (color, brushstrokes, etc.) --the most basic building blocks-- of painting. Purely abstract art, also called "non-representational" or "non-objective" art, contains no identifiable objects or places. With lines, shapes, and colors, pure abstraction can suggest emotion and action, concentrating on the relationships between forms and colors. Very often, the abstract artist paints landscapes, people, and other familiar subjects using simplified or only vaguely recognizable forms. In this case, a subject is described as "abstracted". We can imagine the forms in an abstract painting to be people huddled together, a landscape, a waterscape or perhaps the abstracted shape of a building.