Concepts for Peirce are mental symbols, so they fall under the general designation of signs. For triadic sign relations in general, then, we are dealing with a triadic relation among (1) objects of signs, (2) signs of objects, and (3) what Peirce calls interpretant signs, or interpretants for short. It is critical to regard the three designations of objects, signs, and interpretants as relational roles not ontological essences. It is also critical to distinguish the following things:
- The extended sign relation as a subset of a cartesian product
- The elementary sign relation as an ordered triple in
- The places forming an ordered triple
- The elements filling those places.
Triangles like the one linked above have long been used to introduce the idea of a triadic sign relation. They have the unintended consequence, however, of leading people to miss all the points I mentioned above. So it’s wise to move quickly on to better pictures and more detailed descriptions.