What is the relationship between ontology and modality - between what there is, and what there could be, must be, or might have been? Bob Hale interwove these two strands of metaphysics throughout his long and distinguished career, putting forward his theses in his book, Necessary Beings: An Essay on Ontology, Modality, and the Relations Between Them (OUP 2013). Hale addressed questions of ontology and modality on a number of fronts: through the development of a Fregean approach to ontology, an essentialist theory of modality, and in his work on neo-logicism in the philosophy of mathematics. The essays in this volume engage with these themes in Hale's work in order to progress our understanding of ontology, modality, and the relations between them. Some directly address questions in modal metaphysics, drawing on ontological concerns, while others raise questions in modal epistemology and of its links to matters of ontology, such as the challenge to give an epistemology of essence. Several essays also engage with questions of what might be called 'modal ontology': the study of whether and what things exist necessarily or contingently. Such issues have an important bearing on the kinds of semantic commitments engendered in logic and mathematics (to the existence of sets, or numbers, or properties, and so on) and the extent to which one's ontology of necessary beings interacts with other plausible assumptions and commitments.

Necessary Existence breaks ground on one of the deepest questions anyone ever asks: why is there anything? The classic answer is in terms of a necessary foundation. Yet, why think that is the correct answer? Pruss and Rasmussen present an original defense of the hypothesis that there is a concrete necessary being capable of providing a foundation for the existence of things. They offer six main arguments, divided into six chapters. The first argument is an up-to-date presentation and assessment of a traditional causal-based argument from contingency. The next five arguments are new "possibility-based" arguments that make use of twentieth-century advances in modal logic. The arguments present possible pathways to an intriguing and far-reaching conclusion. The final chapter answers the most challenging objections to the existence of necessary things.

In Necessary Existence and the Doctrine of Being in Avicenna’s Metaphysics of the Healing Daniel De Haan examines the primary notions being, thing, one, and necessary and their roles in the central argument of Avicenna’s metaphysical masterpiece.