Final answer:
Henri Matisse's 'Study of a Women's Back' focuses primarily on the element of shape, which is a two-dimensional form usually outlined by a line or a change in color, distinct from other elements like color or line.
Step-by-step explanation:
Henri Matisse primarily focused on shape in his piece 'Study of a Women's Back'. While color and line are significant in Matisse's work, in this specific instance, it would be the shapes that are particularly noteworthy. According to the principles of art, shape is defined as the property of a two-dimensional form, usually outlined by a line or a change in color. In the case of Matisse and similar artists of his era, the interest in simplifying forms into geometric or organic shapes was a common theme, as evidenced by the treatment of figure and negative space in their works.
In the broader context of art, different elements serve various purposes. For instance, the artists like Piet Mondrian used geometric shapes extensively, emphasizing the role shapes play in composition. Similarly, Anuszkiewicz created illusionary images with patterns and parallel colored lines, demonstrating the versatility of shape and line in creating visual effects. In sculpture, we see these elements combined with spatial relationships to define volume and surface quality, further illustrating the interplay between line, shape, and space.