 The derivability of the necessity of identity from the axioms of identity and the rule of necessitation may perhaps invite one to consider another option. Maybe the culprit is not pure quantificational logic, but rather the indiscriminate use of the rule of necessitation. The rationale for necessitation is that every provable sentence should be necessarily true, but it is not clear how this thought is supposed to generalize to open formulas, which, strictly speaking, are not true or false. Open formulas are merely true or false under an assignment of values to their free variables. But the fact that \(x = x\), for example, is true under an assignment \(s\) on which \(x\) is assigned a table is no reason to think that \(x = x\) is necessarily true under such an assignment if you think that the table could have not been there.[29] One problem for this strategy is that it is of little help when we allow closed terms such as constant symbols into the language of quantified modal logic. In the presence of constant symbols, classical quantificational logic allows us to derive the sentence \(\exists x (a = x)\) as a theorem, whence, by necessitation for complete sentences, we infer \(\Box \exists x(a = x)\), which seems objectionable if \(a\) is suppose to regiment a name for an object that exists only contingently. One could avoid the problems by barring closed terms from the language, but such a radical exclusion seems ad hoc and artificial. So, if one chooses to restrict necessitation, one must provide a different rationale for it. Deutsch (1990) provides an example of this strategy.