The Arnolfini Marriage, Jan van Eyck 1434 (82 x 60 cm).
In Early Netherlandish Painting , on The Arnolfini Marriage, Erwin Panofsky made important contributions to the study of iconography.
Primary or natural subject matter: The most basic level of understanding, this stratum consists of perception of the work’s pure form. Take, for example, a painting of the Last Supper. If we stopped at this first stratum, such a picture could only be perceived as a painting of 13 men seated at a table. This first level is the most basic understanding of a work, devoid of any added cultural knowledge.
Secondary or conventional subject matter (iconography): This stratum goes a step further and brings to the equation cultural and iconographic knowledge. For example, a Western viewer would understand that the painting of 13 men around a table would represent the Last Supper. Similarly, a representation of a haloed man with a lion could be interpreted as a depiction of St. Mark.
Tertiary or intrinsic meaning or content (iconology): This level takes into account personal, technical, and cultural history into the understanding of a work. It looks at art not as an isolated incident, but as the product of a historical environment. Working in this stratum, the art historian can ask questions like “why did the artist choose to represent The Last Supper in this way?” or “Why was St. Mark such an important saint to the patron of this work?” Essentially, this last stratum is a synthesis; it is the art historian asking "what does it all mean?"