Juxtaposition
Dark or light, feminine or masculine, north or south, and night or day. According to Chinese philosophy, there are two opposing but complementary forces or principles found in all non-static objects and processes in the universe--the Yin and Yang. This ever-changing combination of negative and positive results in a state of balance which keeps the world spinning and creates Chi--the life-giving force. For the enterprising photographer, this worldly dichotomy can be viewed from another perspective and translated into a compositional element to enhance the effectiveness of any image.
Juxtaposition, or the visual equivalent of the Yin-Yang concept, allows photographers the opportunity to communicate a disparate situation instantly or inject humor/irony into a dull/mundane moment. From the combinations of the dejected baseball pitcher and jubilant homering baserunner, to the frost-bitten snow shoveler and bikini-clad sunbathers on a background billboard, this tried and true method remains steadfastly powerful. However, on some occasions, a more subtle approach to juxtaposition can be equally rewarding such as this example of a "cat and mouse" for an information systems help-desk pamphlet.
But whatever the case, remember this: all forces in nature can be seen as having Yin and Yang states, and it's imperative for the photographer, through Juxtaposition, to clearly delineate those differences.