Bibliography

On the Foundations of Mathematics

Such a sign whose significance lies in the qualities of its replicas in themselves is an icon, image, analogue, or copy. Its object is whatever that resembles it its interpretant takes it to be the sign of, and is as sign of that object in proportion as it resembles it.

The reference of a sign to its object is brought into special prominence in a kind of sign whose fitness to be a sign is due to its being in a real reactive relation, – generally, a physical and dynamical relation, – with the object. Such a sign I term an index.

A third kind of sign, which brings the reference to an interpretant into prominence[,] is one which is fit to be a sign, not at all because of any particular analogy with the qualities that it signifies, nor because it stands in any reactive relation with its object, but simply and solely because it will be interpreted to be a sign. I call such a sign a symbol.