The Commens Dictionary
Quote from ‘New Elements (Kaina stoiceia)’
It is remarkable that while neither a pure icon nor a pure index can assert anything, an index which forces something to be an icon, as a weathercock does, or which forces us to regard it as an icon, as the legend under a portrait does, does make an assertion, and forms a proposition. This suggests the true definition of a proposition, which is a question in much dispute at this moment. A proposition is a sign which separately, or independently, indicates its object.