The Varieties of Necessity

Necessity abounds. There are the necessary truths of logic, mathematics and metaphysics, the necessary connections among events in the natural world, the necessary or unconditional principles of ethics, and many other forms of necessary truth or connection. But how much diversity is there to this abundance? Are all necessary truths and connections reducible to a single common form of necessity? And if not, then what are the different ways in which a truth might be necessary or a necessary connection might hold? It is the aim of this paper to show that diversity prevails. I shall argue that there are three main forms of necessity the metaphysical, the natural and the normative and that none of them is reducible to the others or to any other form of necessity. Thus what it is for a necessity or possibility of any of these forms to obtain does not consist in the obtaining of some other form or forms of necessity or possibility. Although the focus of the paper falls squarely within the philosophy of modality, some of my arguments may be of broader interest. For certain currently fashionable views on scientific essentialism and ethical naturalism entail the collapse of forms of necessity that I would wish to keep distinct. Thus I have found it essential to indicate what it is in these views that I take to be in error; and this has required consideration of questions from within the metaphysics of natural kinds and the epistemology of ethical belief.