What principle of art involves differences that create visual interest?

Contrast is the principle of art that involves placing differences side by side to create visual interest. It occurs when opposing elements - such as light and dark values, warm and cool colours, rough and smooth textures, large and small shapes, or thick and thin lines - are juxtaposed. These differences draw the viewer's attention and prevent an artwork from appearing flat or monotonous.

Emphasis is about making a particular element stand out as a focal point; while contrast can be used to achieve emphasis, emphasis is about dominance of one area rather than the broader use of differences throughout a work. Harmony is the opposite concept - it involves combining similar or related elements to create a pleasing, consistent look. Balance concerns the distribution of visual weight across a composition (symmetrical, asymmetrical, or radial), not the use of differences to generate interest.

The question specifically asks about "differences that create visual interest," which directly defines contrast as a principle of art.