Peirce’s fundamental typology of signs exhibits a property capable of functioning as a conceptual criterion to distinguish different kinds of signs: the relative dependence of sign-object-interpretant (S-O-I) components in triadic relation (S-O-I). A symbol is an S-O relationship logically dependent of I (CP 2.307). In a different way, an index is dependent of O. Constraints resulting from the space-time existence of the object represented by the index are irrelevant in symbolic processes. Icons, in turn, are deeply dependent on the material, form and structure that they are made of – “An Icon is a sign which refers to the Object that it denotes merely by virtue of characters of its own, and which it possesses, just the same, whether any such Object actually exists or not” (CP 2.247).
According to this basic criterion, the icon is the only type of sign which is S-dependent (that means, dependent on the sign material and structural organization itself) and is able to reveal, through its manipulation, some information about the object. This operational property of iconicity is considered a detrivilization of the notion that the icon is fundamentally based on a relation of similarity.
According to Chris Hookway (2000: 102),
“The key of iconicity is not perceived resemblance between the sign and what it signifies but rather the possibility of making new discoveries about the object of a sign through observing features of the sign itself.”
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