The Commens Dictionary
Quote from ‘Harvard Lectures on Pragmatism: Lecture III’
A degenerate Index is a representamen which represents a single object because it is factually connected with it, but which conveys no information whatever. Such, for example, are the letters attached to a geometrical or other diagram. A proper name is substantially the same thing; for although in this case the connection of the sign with its object happens to be a purely mental association, yet that circumstance is of no importance in the functioning of the representamen. The use of letters as indices is not confined to mathematics. Lawyers particularly often discuss cases in which A contracts with B to do something. These letters are convenient substitutes for relative pronouns. A relative, demonstrative, or personal pronoun comes very near to being a mere Index, if it be not accurately so. It is far more correct so to define it than to say that a pronoun is a word placed instead of a noun. It would be nearer right to say that a common noun when subject nominative is a word put in place of a pronoun. A degenerate index may be called a Monstrative Index, in contradistinction to an Informational or Genuine Index.