Necessarily, salt dissolves in water
In this paper I aim to show that a certain law of nature, namely that common salt (sodium chloride) dissolves in water, is metaphysically necessary. The importance of this result is that it conflicts with a widely shared intuition that the laws of nature (most if not all) are contingent. There have been debates over whether some laws, such as Newton’s second law, might be definitional of their key terms and hence necessary. But the law that salt dissolves in water is not that kind of law. The law statement ‘salt dissolves in water’ is clearly synthetic. It appears a classic case of a contingent law. We like to believe that there are possible worlds in which the laws of nature are different and in which salt does not dissolve in water. Showing that our intuition about the contingency of this law is mistaken reinforces two lessons of Kripke’s well-known arguments concerning necessity and identity: that our untutored intuitions concerning modal status are unreliable and that there is more necessity around than we might think (Kripke 1980). The result has further significance also. Dispositional essentialists (dispositionalists, for short) about properties are committed to regarding the laws of nature as metaphysically necessary ‐ they are necessitarians about laws. 1 Their critics, who are categoricalists about properties and contingentists about laws, regard this as a major disadvantage, as conflicting with a deep intuition that laws are mostly contingent. If it can be shown, independently of dispositionalism, that some apparently contingent laws are in fact necessary, then this objection loses its force. The premisses of the argument I present should be acceptable to contingentists. It assumes that the basic laws of nature are contingent. It then shows that some laws that supervene on the basic ones will not themselves be contingent. One lesson for contingentists is that they cannot be contingentist about all laws, not even all synthetic, a posteriori laws. Overall, the argument may be seen as a disjunctive dilemma. Either the basic laws are necessary, in which case those that supervene on them are necessary; or the