 The exclusive relation that holds between incompatible actions also provides a context for Royce’s notion of equivalence (Royce 1905, 391). An action, \(A\), is logically equivalent to another action, \(B\), if and only if they are compatible (one can be taken without excluding the other). So, for example, if \(A\) and \(B\) are compatible and \(B\) and \(\neg B\) are incompatible, then \(A\) and \(\neg B\) are also incompatible. If so, then \(A = B\). In the case of voting just mentioned, the three-term relation (voting for candidate \(M\), voting for someone else, and not voting at all) are together incompatible. If we consider the first option, voting for \(M\), then the other two options are equivalent because they equally eliminate voting for \(M\) if one or the other is taken. Equivalence then is relative to compatibility in a given situation defined by a set of incompatible or “obverse” possibilities.