What is the relation between metaphysical necessity and essence? This paper defends the view that the relation is one of identity: metaphysical necessity is a special case of essence. My argument consists in showing that the best joint theory of essence and metaphysical necessity is one in which metaphysical necessity is just a special case of essence. The argument is made against the backdrop of a novel, higher-order logic of essence (HLE), whose core features are introduced in the first part of the paper. The second part investigates the relation between metaphysical necessity and essence in the context of HLE. Reductive hypotheses are among the most natural hypotheses to be explored in the context of HLE. But they also have to be weighed against their non-reductive rivals. I investigate three different reductive hypotheses and argue that two of them fare better than their non-reductive rivals: they are simpler, more natural, and more systematic. Specifically, I argue that one candidate reduction, according to which metaphysical necessity is truth in virtue of the nature of all propositions, is superior to the others, including one proposed by Kit Fine, according to which metaphysical necessity is truth in virtue of the nature of all objects. The paper concludes by offering some reasons to think that the best joint theory of essence and metaphysical necessity is one in which the logic of metaphysical necessity includes S4, but not S5.

形而上的必然性与本质的关系是什么？本文捍卫了关系是同一性的观点：形而上学必然性是本质的一个特例。我的论点在于表明，关于本质和形而上学必然性的最佳联合理论是形而上学必然性只是本质的一个特例。该论点是在一种新颖的高阶本质逻辑（HLE）的背景下进行的，其核心特征在论文的第一部分中进行了介绍。第二部分探讨了HLE语境下形而上学必然性与本质的关系。还原假设是在HLE的背景下探索的最自然的假设之一. 但它们也必须与非还原性竞争对手进行权衡。我研究了三个不同的还原假设，并认为其中两个比它们的非还原对手更好：它们更简单、更自然、更系统。具体来说，我认为一种候选还原（根据所有命题的性质，形而上学必然性是真理）优于其他还原，包括由 Kit Fine 提出的，根据这种还原，形而上学必然性是由于性质而为真所有对象。文章最后给出了一些理由，认为最好的本质和形而上学必然性结合理论是形而上学必然性的逻辑包括S4但不包括S5的理论。