…Thirdness, or that which is such as it is in bringing a second into relation to a third. That thirdness cannot be reduced to any combination of secondnesses follows at once from the fact that combination is itself a triadic relation; so that a combination of secondnesses would itself involve an irreducible thirdness.On the other hand, [there] can be no irreducible Fourthness or mode of being defined by a relation between more than three correlates, since it is easily shown that every such relation is definable as a triadic relation among triadic relations.