What ways shadows and light define the mass of forms in art?

Shadows and light play a crucial role in defining the mass of forms in art by creating contrast and depth, which help to suggest three-dimensionality on a two-dimensional surface. Light illuminates certain areas, highlighting contours and textures, while shadows recede parts of the form, adding volume and weight. This interplay enhances the perception of solidity and spatial relationships, guiding the viewer's eye and shaping their understanding of the depicted objects. Ultimately, the effective use of light and shadow can evoke emotions and create a dynamic sense of realism in artistic compositions.