The middle ground between relations in general and the sign relations we need to do logic, inquiry, communication, and so on is occupied by triadic relations, also called ternary or 3-place relations.

Triadic relations are some of the most pervasive in mathematics, over and above the importance of sign relations for logic.

Here’s a primer with examples from mathematics and semiotics:

• Triadic Relations • OEIS Wiki • Wikiversity

cc: Ontolog Forum • Structural Modeling • Systems Science