A photograph seems to match C.S. Peirce’s definition of a sign perfectly: “something which stands to somebody for something in some respect or capacity” (C.P. 2:228, emphasis mine). If it stands for something (whether an optical reality, or an artistic conception) in what respect or capacity does it operate? A photograph seems to operate simultaneously on the metaphoric and metonymic poles. It alludes to a contiguity with a subject which once existed before the camera. It also represents a discontinuity, an artificial representation of a subject outside our immediate view. If a photograph (as a thing) always has a relationship with another thing, how might we describe it?

Aristotle proposes in Categories that things that have only a name in common with a different definition of being corresponding to each are called homonymous. The example he uses is confusing when translated into English:

Thus, for example, both a man and a picture are animals. These have only a name in common and the definition of being which corresponds to the name is different; for to say what being an animal is for each of them, one will give two distinct definitions.

J.L. Ackrill, like most translators, has translated the Greek zôion as animal. The term, in Greek, is applied to pictures or illustrations in the same sense we use the word figure in English—a picture is a figure, and a man has a figure. Another translation in the public domain by EM Edghill avoids the confusion by saying “a figure in a picture” in place of “picture,” which does not really express the same concept.

The concept of homonymy applied to things is different from the concept applied to words. Two words which sound the same but mean different things are called homonyms. In the case of an object and its photograph, one might say that they look the same but they mean different things. The major evidentiary fallacy regarding photographs might be that they are regarded as synonymous rather than homonymous.

One of the primary failings of homonyms is that they seldom remain homonyms after translation. If descriptive language is attached to a photograph, it amounts to a translation of the visual evidence apparent in the photograph. A good description can be synonymous with a photograph, but it complicates the homonymous relation that a photograph has with its subject. The primary relationship between photograph and subject is perhaps untranslatable. However, if this is the case then the photograph violates a primary condition of linguistic signs—that they be translatable.