What are the main shapes in a painting

The main shapes would be the objects in the painting that are drawn as actual physical objects being within the setting of the painting. They are called positive shapes. They are actually present in the setting of the painting and do not represent any additional themes. They may be present to be open to interpretation, but they are "there" regardless. An example would be a single empty chair on a beach - it can be interpreted in many ways but the actual chair is on an actual beach within the setting of the painting.