Peirce's Diagrammatic Solutions to 'Peirce's Puzzle'

We present Peirce's own solution to what is known as 'Peirce's Puzzle' in formal semantics and pragmatics. In his mostly unpublished writings, Peirce analyses some sentences in the modal extension of his Beta Existential Graphs (that is, in a diagrammatic system of quantified first-order logic with tinctures) and in algebraic logic. These diagrams represent the pragmatic idea of information states that support or fail to support sentences with (non-existential) indefinites and modalities. The interpretation of such sentences presupposes a graphic-pragmatic criterion of cross-identification.