Final answer:
In art, shading assists in creating the appearance of solidity of form on a two-dimensional surface, providing depth and volume, and thus enhances the realism of the drawing.
Step-by-step explanation:
In art, when shading is applied to a drawing, it primarily helps achieve the effect of solidity of form. Shading provides the illusion of depth and volume on a two-dimensional surface, which brings a sense of reality to the drawing. The use of light and shadow strategically can direct attention and create a mood. For instance, in a landscape painting, atmospheric perspective may be employed to give a sense of recession in space, and the direction of light can profoundly affect how solid objects appear with the creation of shadows giving a three-dimensional feeling. Artists like Albert Bierstadt have used these techniques to portray the expansiveness of landscapes such as in his painting 'The Rocky Mountains, Lander's Peak'.