I conclude from the examination of an example of semiosis that even though Peirce himself typically talks of two types of causation being involved, usually referred to as 'efficient' and 'final,' he could have-and for completeness should have-spoken of three types, the third corresponding to the classical conception of 'formal' causation. (A Peircean modification of the classical four-cause scheme requires abandonment of the notion of the fourth or 'material' cause as that was understood by Aristotle. This fourth factor has no functional counterpart in Peirce's philosophy because its function in the explanation of natural processes was bound up with the cyclical character of Aristotle's conception of such processes, which has no appropriately close parallel in Peirce's philosophy at the level of the generic conception of a sign.) The following is not textual exegesis and no textual basis is cited for it since it is based rather on my overall understanding of semiosis, as I have acquired that from studying Peirce.