The Commens Dictionary
Quote from ‘Notes on Portions of Hume's "Treatise on Human Nature"’
It is difficult to define a sign in general. It is something which is in such a relation to an object that it determines, or might determine, another sign of the same object. This is true but considered as a definition it would involve a vicious circle, since it does not say what is meant by the interpretant being a “sign” of the same object. However, this much is clear; that a sign has essentially two correlates, its Object and its possible Interpretant sign. Of these three, Sign, Object, Interpretant, the Sign as being the very thing under consideration is Monadic, the Object is Dyadic, and the Interpretant is Triadic. We therefore look to see, whether there be not two Objects and three Interpretants. There obviously are two Objects, the object as it is in itself (the Monadic Object), and the object as the sign represents it to be (the Dyadic Object). There are also three Interpretants; namely, 1st, the Interpretant considered as an independent sign of the Object, 2nd, the Interpretant as it is as a fact determined by the Sign to be, and 3rd the Interpretant as it is intended by, or is represented in, the Sign to be.